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Use the commands in this chapter to configure and monitor Intermediate System-to-Intermediate System (IS-IS) protocol. For IS-IS configuration information and examples, refer to the "Configuring Integrated IS-IS" chapter of the Cisco IOS IP and IP Routing Configuration Guide.
To configure the Intermediate System-to-Intermediate System (IS-IS) area authentication password, use the area-password router configuration command. To disable the password, use the no form of this command.
area-password password
Syntax Description
password Password you assign.
Defaults
No area password is defined and area password authentication is disabled.
Command Modes
Router configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
Using the area-password command on all routers in an area will prevent unauthorized routers from injecting false routing information into the linkstate database.
This password is exchanged as plain text and thus this feature provides only limited security.
This password is inserted in Level 1 (station router level) link state PDUs (LSPs), complete sequence number PDUs (CSNPs), and partial sequence number PDUs (PSNP).
Examples
The following example assigns an area authentication password:
router isisarea-password angel
Related Commands
Configures the IS-IS routing domain authentication password. Configures the authentication password for an interface.
Command
Description
To generate a default route into an Intermediate System-to-Intermediate System (IS-IS) routing domain, use the default-information originate router configuration command. To disable this feature, use the no form of this command.
default-information originate [route-map map-name]
Syntax Description
route-map map-name (Optional) Routing process will generate the default route if the route map is satisfied.
Defaults
Disabled
Command Modes
Router configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
If a router configured with this command has a route to 0.0.0.0 in the routing table, IS-IS will originate an advertisement for 0.0.0.0 in its link-state packets (LSPs).
Without a route-map, the default is only advertised in L2 LSPs. For L1 routing, there is another mechanism to find the default route, which is to look for the closest L1L2 router. The closest L1L2 router can be found by looking at the attached-bit (ATT) in L1 LSPs.
A route-map can be used for two things: 1) make the router generate default in its L1 LSPs.
2) advertise 0/0 conditionally. With a match ip address standard-access-list command, you can specify one or more IP routes that must exist before the router will advertise 0/0.
Examples
The following example forces the software to generate a default external route into an IS-IS domain:
router isis ! BGP routes will be distributed into IS-IS redistribute bgp 120 ! access list 2 is applied to outgoing routing updates distribute-list 2 out default-information originate ! access list 2 defined as giving access to network 100.105.0.0 access-list 2 permit 100.105.0.0 0.0.255.255
Related Commands
redistribute Redistributes routes from one routing domain into another routing domain. Displays the IS-IS link state database.
Command
Description
To configure the Intermediate System-to-Intermediate System (IS-IS) routing domain authentication password, use the domain-password router configuration command. To disable a password, use the no form of this command.
domain-password password
Syntax Description
password Password you assign.
Defaults
No password is specified and no authentication is enabled for exchange of L2 routing information.
Command Modes
Router configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
This password is exchanged as plain text and thus this feature provides only limited security.
This password is inserted in Level 2 (area router level) link state PDUs (LSPs), complete sequence number PDUs (CSNPs), and partial sequence number PDUs (PSNPs).
Examples
The following example assigns an authentication password to the routing domain:
router isis domain-password flower
Related Commands
Configures the IS-IS area authentication password. Configures the authentication password for an interface.
Command
Description
To configure an Intermediate System-to-Intermediate System (IS-IS) routing process for IP on an interface and to attach an area designator to the routing process, use the ip router isis interface configuration command. Use the no form of the command to disable IS-IS for IP.
ip router isis area-tag
Syntax Description
area-tag Required for multiarea IS-IS configuration. Optional for conventional IS-IS configuration. Defines a meaningful name for an area routing process. If not specified, a null tag is assumed. It must be unique among all IP router processes for a given router. The area-tag argument is used later as a reference to this area routing process. Each area in a multiarea configuration should have a nonnull area tag to facilitate identification of the area.
Defaults
No routing processes are specified.
Command Modes
Interface configuration
Command History
10.0 This command introduced. 12.0(5)T Multiarea functionality was added, changing the way the tag argument (now area-tag) is used.
Release
Modification
Usage Guidelines
Before the IS-IS routing process is useful, a network entity title (NET) must be assigned with the net command and some interfaces must have IS-IS enabled.
If you have IS-IS running and at least one ISO-Interior Gateway Routing Protocol (IGRP) process, the IS-IS process and the ISO-IGRP process cannot both be configured without an area tag. The null tag can be used by only one process. If you run ISO-IGRP and IS-IS, a null tag can be used for IS-IS, but not for ISO-IGRP at the same time. However, each area in an IS-IS multiarea configuration should have a nonnull area tag to facilitate identification of the area.
You can configure only one process to perform Level 2 (interarea) routing. If Level 2 routing is configured on any process, all additional processes are automatically configured as Level 1. You can configure this process to perform intra-area (Level 1) routing at the same time. You can configure up to 29 additional processes as Level 1-only processes. Use the is-type command to remove Level 2 routing from a router instance. You can then use the is-type command to enable Level 2 routing on some other IS-IS router instance.
An interface cannot be part of more than one area, except in the case where the associated routing process is performing both Level 1 and Level 2 routing. On media (such as WAN media, for example) where subinterfaces are supported, different subinterfaces could be configured for different areas.
Examples
The following example specifies IS-IS as an IP routing protocol for a process named Finance, and specifies that the Finance process will be routed on interfaces Ethernet 0 and serial 0:
router isis Finance net 49.0001.aaaa.aaaa.aaaa.00 interface Ethernet 0 ip router isis Finance interface serial 0 ip router isis Finance
The following example shows an IS-IS configuration with two Level 1 areas and one Level 1-2 area:
ip routing ... interface Tunnel529 ip address 10.0.0.5 255.255.255.0 ip router isis BB interface Ethernet1 ip address 10.1.1.5 255.255.255.0 ip router isis A3253-01 1 ! interface Ethernet2 ip address 10.2.2.5 255.255.255.0 ip router isis A3253-02 ... ! Defaults to "is-type level-1-2" router isis BB net 49.2222.0000.0000.0005.00 ! router isis A3253-01 net 49.0553.0001.0000.0000.0005.00 is-type level-1 ! router isis A3253-02 net 49.0553.0002.0000.0000.0005.00 is-type level-1
Related Commands
Configures an IS-IS network entity title (NET) for the routing process. Enables the IS-IS routing protocol.
Command
Description
To configure the type of adjacency, use the isis circuit-type interface configuration command. To reset the circuit type to Level l and Level 2, use the no form of this command.
isis circuit-type {level-1 | level-1-2 | level-2-only}
Syntax Description
level-1 A Level 1 adjacency may be established if there is at least one area address in common between this system and its neighbors. Level 2 adjacencies will never be established over this interface. level-1-2 A Level 1 and Level 2 adjacency is established if the neighbor is also configured as level-1-2 and there is at least one area in common. If there is no area in common, a Level 2 adjacency is established. This is the default. level-2-only Level 2 adjacencies are established if the other routers are Level 2 or Level 1-2 routers and their interfaces are configured for Level 1-2 or Level 2. Level 1 adjacencies will never be established over this interface.
Defaults
A Level 1 and Level 2 adjacency is established.
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
Normally, this command does not need to be configured. The proper way is to configure a router as an Level 1-only, Level 1-2 or Level 2-only system. Only on routers that are between areas (Level 1-2 routers) should you configure some interfaces to be Level 2-only to prevent wasting bandwidth by sending out unused Level 1 hellos. Note that on point-to-point interfaces, the Level 1 and Level 2 hellos are in the same packet.
Examples
In the following example, other routers on Ethernet interface 0 are in the same area. Other routers on Ethernet interface 1 are in other areas, so the router will stop sending Level 1 hellos.
interface ethernet 0 ip router isis interface ethernet 1 isis circuit-type level-2-only
To configure the Intermediate System-to-Intermediate System (IS-IS) complete sequence number PDUs (CSNP) interval, use the isis csnp-interval interface configuration command. To restore the default value, use the no form of this command.
isis csnp-interval seconds {level-1 | level-2}
Syntax Description
seconds Interval of time between transmission of CSNPs on multiaccess networks. This interval only applies for the designated router. The default is 10 seconds. level-1 Configures the interval of time between transmission of CSNPs for Level 1 independently. level-2 Configures the interval of time between transmission of CSNPs for Level 2 independently.
Defaults
10 seconds
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
It is very unlikely you will need to change the default value of this command.
This command only applies for the designated router (DR) for a specified interface. Only DRs send CSNP packets in order to maintain database synchronization. The CSNP interval can be configured independently for Level 1 and Level 2. This feature does not apply to serial point-to-point interfaces. It does apply to WAN connections if the WAN is viewed as a multiaccess meshed network.
For multi-access WAN interfaces (such as ATM, Frame Relay, and X.25), it is highly recommended you configure the NBMA cloud as multiple point-to-point subinterfaces. Doing so will make routing much more robust if one or more PVCs fail.
The isis csnp-interval command on point-to-point subinterfaces only makes sense when using it in combination with the IS-IS mesh-group feature.
Examples
The following example configures Ethernet interface 0 for sending CSN PDUs every 30 seconds.
interface ethernet 0 isis csnp-interval 30 level-1
To make output from multiarea displays easier to read by specifying the delimiter to use to separate displays of information, use the isis display delimiter global configuration command. This command displays the output from different areas as a string or additional white space. Use the no form of the command to disable this output format. cnt
isis display delimiter [return cnt | char cnt]
Syntax Description
return (Optional) Delimit with carriage returns. cnt (Optional) Number of carriage returns or length of string to use for delimiter. char (Optional) Character to use for delimiter string.
Defaults
By default the isis display delimiter command is disabled.
Command Modes
Global configuration
Command History
12.0(5)T This command was introduced.
Release
Modification
Usage Guidelines
Use this command to customize display output when the IS-IS multiarea feature is used.
Examples
The following command causes different areas in multiarea displays (such as show command output) to be delimited by a string of dashes (-):
isis display delimiter - 14
With three IS-IS neighbors configured, this command displays the following output from the show clns neighbors command:
dtp-5# show clns neighbors -------------- Area L2BB: System Id Interface SNPA State Holdtime Type Protocol 0000.0000.0009 Tu529 172.21.39.9 Up 25 L1L2 IS-IS -------------- Area A3253-01: System Id Interface SNPA State Holdtime Type Protocol 0000.0000.0053 Et1 0060.3e58.ccdb Up 22 L1 IS-IS 0000.0000.0003 Et1 0000.0c03.6944 Up 20 L1 IS-IS -------------- Area A3253-02: System Id Interface SNPA State Holdtime Type Protocol 0000.0000.0002 Et2 0000.0c03.6bc5 Up 27 L1 IS-IS 0000.0000.0053 Et2 0060.3e58.ccde Up 24 L1 IS-IS
Related Commands
show clns es-neighbors Lists the ES neighbors that this router knows. show clns is-neighbors Displays IS-IS related information for IS-IS router adjacencies. show clns neighbors Displays both ES and IS neighbors. show clns protocol Lists the protocol-specific information for each ISO IGRP routing process in the router. show clns traffic Lists the CLNS packets this router has seen. Displays the IS-IS link-state database. show isis routes Displays the IS-IS Level 1 forwarding table for IS-IS learned routes. Displays how often and why the router has run a full SPF calculation. Displays a list of all connected routers in all areas.
Command
Description
To specify the length of time between hello packets that the Cisco IOS software sends, use the isis hello-interval interface configuration command. To restore the default value, use the no form of this command.
isis hello-interval seconds {level-1 | level-2}
Syntax Description
seconds An integer value. By default, a value three times the hello interval seconds is advertised as the holdtime in the hello packets sent. (That multiplier of 3 can be changed by specifying the isis hello-multiplier command.) With smaller hello intervals, topological changes are detected faster, but there is more routing traffic. The default is 10 seconds. level-1 Configures the hello interval for Level 1 independently. Use this on X.25, Switched Multimegabit Data Service (SMDS), and Frame Relay multiaccess networks. level-2 Configures the hello interval for Level 2 independently. Use this on X.25, SMDS, and Frame Relay multiaccess networks.
Defaults
10 seconds
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
The hello interval can be configured independently for Level 1 and Level 2, except on serial point-to-point interfaces. (Because there is only a single type of hello packet sent on serial links, it is independent of Level 1 or Level 2.) The level-1 and level-2 keywords are used on X.25, SMDS, and Frame Relay multiaccess networks or LAN interfaces.
A faster hello interval gives faster convergence, but increases bandwidth and CPU usage. It might also add to instability in the network. A slower hello interval saves bandwidth and CPU. Especially when used in combination with a higher hello multiplier, this may increase overall network stability.
It makes more sense to tune the hello interval and hello multiplier on point-to-point interfaces than on LAN interfaces.
Examples
The following example configures serial interface 0 to advertise hello packets every 5 seconds. The router is configured to act as a station router. This will cause more traffic than configuring a longer interval, but topological changes will be detected faster.
interface serial 0 isis hello-interval 5 level-1
Related Commands
Specifies the number of IS-IS hello packets a neighbor must miss before the router should declare the adjacency as down.
Command
Description
To specify the number of Intermediate System-to-Intermediate System (IS-IS) hello packets a neighbor must miss before the router should declare the adjacency as down, use the isis hello-multiplier interface configuration command. To restore the default value, use the no form of this command.
isis hello-multiplier multiplier {level-1 | level-2}
Syntax Description
multiplier Integer value from 3 to 1000. The advertised holdtime in IS-IS hellos will be set to the hello-multiplier times the hello-interval. Neighbors will declare an adjacency to this router down after not having received any IS-IS hellos during the advertised holdtime. The holdtime (and thus the hello-multiplier and the hello-interval) can be set on a per interface basis, and can be different between different routers in one area. Using a smaller hello-multiplier will give fast convergence, but can result in more routing instability. Increment the hello-multiplier to a larger value to help network stability when needed. Never configure a hello-multiplier lower then the default value of 3. level-1 Configures the hello multiplier independently for Level 1 adjacencies. level-2 Configures the hello multiplier independently for Level 2 adjacencies.
Defaults
multiplier is 3
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
The "holding time" carried in an IS-IS hello packet determines how long a neighbor waits for another hello packet before declaring the neighbor to be down. This time determines how quickly a failed link or neighbor is detected so that routes can be recalculated.
Use the isis hello-multiplier command in circumstances where hello packets are lost frequently and IS-IS adjacencies are failing unnecessarily. You can raise the hello multiplier and lower the hello interval (isis hello-interval command) correspondingly to make the hello protocol more reliable without increasing the time required to detect a link failure.
On point-to-point links, there is only one hello for both Level 1 and Level 2, so configuring different hello-multipliers only makes sense for multi-access networks, such as Ethernet, FDDI, etc. Separate Level 1 and Level 2 hellos are also sent over NBMA networks in multipoint mode, such as X.25, Frame Relay and ATM. However, it is recommended to run IS-IS over point-to-point subinterfaces over WAN NBMA media.
Examples
In the following example, the network administrator wants to increase network stability by making sure an adjacency will go down only when many (10) hellos are missed. The total time to detect link failure is 60 seconds. This will ensure that the network remains stable, even when the link is fully congested.
interface serial 1 ip router isis isis hello-interval 6 level-1 isis hello-multiplier 10 level-1
Related Commands
Specifies the length of time between hello packets that the Cisco IOS software sends.
Command
Description
To configure the time delay between successive Intermediate System-to-Intermediate System (IS-IS) link state packet transmissions, use the isis lsp-interval interface configuration command. To restore the default value, use the no form of this command.
isis lsp-interval milliseconds
Syntax Description
milliseconds Time delay between successive link state packets, in milliseconds.
Defaults
The default time delay is 33 milliseconds.
Command Modes
Interface configuration
Command History
11.1 This command was introduced.
Release
Modification
Usage Guidelines
In topologies with a large number of IS-IS neighbors and interfaces, a router may have difficulty with the CPU load imposed by link state packet (LSP) transmission and reception. This command allows the LSP transmission rate (and by implication the reception rate of other systems) to be reduced.
Examples
The following example causes the system to send LSPs every 100 milliseconds (10 packets per second) on serial interface 0:
interface serial 0 isis lsp-interval 100
Related Commands
Configures the time between retransmission of each LSP (IS-IS link state PDU) over point-to-point links.
Command
Description
To optimize link-state packet (LSP) flooding in nonbroadcast multiaccess (NBMA) networks with highly meshed, point-to-point topologies, use the isis mesh-group interface configuration command. To remove a (sub)interface from a mesh group, use the no form of this command.
isis mesh-group [num | blocked]
Syntax Description
num (Optional) A number identifying the mesh group of which this interface is a member. blocked (Optional) Keyword specifying that no LSP flooding will take place on this (sub)interface.
Defaults
The interface performs normal flooding.
Command Modes
Interface configuration
Command History
12.0 This command was introduced.
Release
Modification
LSPs that are first received on (sub)interfaces that are not part of a mesh group are flooded to all other (sub)interfaces in the usual way.
LSPs that are first received on (sub)interfaces that are part of a mesh group are flooded to all interfaces except those in the same mesh-group. If the "blocked" keyword is configured on a (sub)interface, then a newly received LSP is not flooded out over that interface.
To minimize the possibility of incomplete flooding, you should allow unrestricted flooding over at least a minimal set of links in the mesh. Selecting the smallest set of logical links that covers all physical paths results in very low flooding, but less robustness. Ideally you should select only enough links to ensure that LSP flooding is not detrimental to scaling performance, but enough links to ensure that under most failure scenarios no router will be logically disconnected from the rest of the network. In other words, blocking flooding on all links permits the best scaling performance, but there is no flooding. Permitting flooding on all links results in very poor scaling performance.
Examples
In the following example six interfaces are configured in three mesh groups. LSPs received are handled as follows:
interface atm 1/0.1
ip router isis
isis mesh-group 10 interface atm 1/0.2 ip router isis
isis mesh-group 10 interface atm 1/1.1
ip router isis
isis mesh-group 11 interface atm 1/1.2
ip router isis
isis mesh-group 11 interface atm 1/2.1
ip router isis isis mesh-group blocked interface atm 1/2.2
ip router isis
Related Commands
Enables the IS-IS routing protocol and specifies an IS-IS process.
Command
Description
To configure the metric for an interface, use the isis metric interface configuration command. To restore the default metric value, use the no form of this command.
isis metric default-metric {level-1 | level-2}
Syntax Description
default-metric Metric assigned to the link and used to calculate the cost from each other router via the links in the network to other destinations. You can configure this metric for Level 1 or Level 2 routing. The range is from 0 to 63. The default value is 10. level-1 This metric should be used only in the SPF calculation for L1 (intra-area) routing. level-2 This metric should be used only in the SPF calculation for L2 (interarea) routing.
Defaults
default-metric = 10
If level-1 or level-2 is not specified, level-1 is assumed.
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
Specifying the level-1 or level-2 keywords resets the metric only for Level 1 or Level 2 routing, respectively.
It is highly recommended to configure metrics on all interfaces. If you do not do so, the IS-IS metrics are similar to hop-count metrics.
Examples
The following example configures serial interface 0 for a default link-state metric cost of 15 for Level 1:
interface serial 0 isis metric 15 level-1
To configure the authentication password for an interface, use the isis password interface configuration command. To disable authentication for Intermediate System-to-Intermediate System (IS-IS), use the no form of this command.
isis password password {level-1 | level-2}
Syntax Description
password Authentication password you assign for an interface. level-1 Configures the authentication password for Level 1 independently. For Level 1 routing, the router acts as a station router only. level-2 Configures the authentication password for Level 2 independently. For Level 2 routing, the router acts as an area router only.
Defaults
Disabled
If no keyword is specified, the default is level-1.
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
This command enables you to prevent unauthorized routers from forming adjacencies with this router, and thus protects the network from intruders.
The password is exchanged as plain text and thus provides only limited security.
Different passwords can be assigned for different routing levels using the level-1 and level-2 keyword arguments.
Specifying the level-1 or level-2 keywords disables the password only for Level 1 or Level 2 routing, respectively.
Examples
The following example configures a password for Ethernet interface 0 at Level 1:
interface ethernet 0 isis password frank level-1
To configure the priority of designated routers, use the isis priority interface configuration command. To reset the default priority, use the no form of this command.
isis priority value {level-1 | level-2}
Syntax Description
value Sets the priority of a router and is a number from 0 to 127. The default value is 64. level-1 Sets the priority for Level 1 independently. level-2 Sets the priority for Level 2 independently.
Defaults
Priority of 64
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
Priorities can be configured for Level 1 and Level 2 independently. Specifying the level-1 or level-2 keywords resets priority only for Level 1 or Level 2 routing, respectively.
The priority is used to determine which router on a LAN will be the designated router or Designated Intermediate System (DIS). The priorities are advertised in the hellos. The router with the highest priority will become the DIS.
In IS-IS, there is no backup designated router. Setting the priority to 0 lowers the chance of this system becoming the DIS, but does not prevent it. If a router with a higher priority comes on line, it will take over the role from the current DIS. In the case of equal priorities, the highest MAC address breaks the tie.
Examples
The following example shows Level 1 routing given priority by setting the priority level to 80. This router is now more likely to become the DIS.
interface ethernet 0 isis priority 80 level-1
To configure the amount of time between retransmission of each Intermediate System-to-Intermediate System (IS-IS) link-state packet (LSP) on a point-to-point link, use the isis retransmit-interval interface configuration command. To restore the default value, use the no form of this command.
isis retransmit-interval seconds
Syntax Description
seconds Time in seconds between retransmission of each LSP. It is an integer that should be greater than the expected round-trip delay between any two routers on the attached network. The default is 5 seconds.
Defaults
5 seconds
Command Modes
Interface configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
The setting of the seconds argument should be conservative, or needless retransmission will result.
This command has no effect on LAN (multipoint) interfaces. On point-to-point links, the value can be increased to enhance network stability.
Retransmissions only occur when LSPs are dropped. So setting this to a higher value has little effect on reconvergence. The more neighbors routers have, and the more paths over which LSPs can be flooded, the higher this value can be made.
The value should be larger for serial lines.
Examples
The following example configures serial interface 0 for retransmission of IS-IS LSP every 60 seconds for a large serial line:
interface serial 0 isis retransmit-interval 60
Related Commands
Configures the time delay between successive IS-IS link state packet transmissions. Configures the amount of time between retransmissions of any IS-IS LSPs on a point-to-point interface.
Command
Description
To configure the amount of time between retransmissions on each Intermediate System-to-Intermediate System (IS-IS) link-state packet (LSP) on a point-to-point interface, use the isis retransmit-throttle-interval interface configuration command. To restore the default value, use the no form of this command.
isis retransmit-throttle-interval milliseconds
Syntax Description
milliseconds Minimum delay (in milliseconds) between LSP retransmissions on the interface.
Defaults
The delay is determined by the isis lsp-interval command.
Command Modes
Interface configuration
Command History
11.1 This command was introduced.
Release
Modification
Usage Guidelines
This command may be useful in very large networks with many LSPs and many interfaces as a way of controlling LSP retransmission traffic. This command controls the rate at which LSPs can be re-sent on the interface.
The isis retransmit-throttle-interval command is distinct from the rate at which LSPs are sent on the interface (controlled by the isis lsp-interval command) and the period between retransmissions of a single LSP (controlled by the isis retransmit-interval command). These commands may all be used in combination to control the offered load of routing traffic from one router to its neighbors.
Examples
The following example configures serial interface 0 to limit the rate of LSP retransmissions to one every 300 milliseconds:
interface serial 0 isis retransmit-throttle-interval 300
Related Commands
Configures the time delay between successive IS-IS link state packet transmissions. Configures the amount of time between retransmission of each IS-IS link-state PDUs (LSPs) over a point-to-point link.
Command
Description
To configure the routing level for an instance of the Intermediate System-to-Intermediate System (IS-IS) routing process, use the is-type router configuration command. To reset the default value, use the no form of this command.
is-type {level-1 | level-1-2 | level-2-only}
Syntax Description
level-1 Router performs only Level 1 (intra-area) routing. This router only learns about destinations inside its area. Level 2 (interarea) routing is performed by the closest Level 1-2 router. level-1-2 Router performs both Level 1 and Level 2 routing. This router runs two instances of the routing process. It has one link-state packet database (LSDB) for destinations inside the area (Level 1 routing) and runs an shortest path first (SPF) calculation to discover the area topology. It also has another link-state packet database (LSDB) with link-state packets (LSPs) of all other backbone (Level 2) routers, and runs another SPF calculation to discover the topology of the backbone, and the existence of all other areas. level-2-only Routing process acts as a Level 2 (interarea) router only. This router is part of the backbone, and does not communicate with Level 1-only routers in its own area.
Defaults
In conventional IS-IS configurations, the router acts as both a Level 1 (intra-area) and a Level 2 (interarea) router.
In multiarea IS-IS configurations, the first instance of the IS-IS routing process configured is by default a Level 1-2 (intra-area and interarea) router. The remaining instances of the IS-IS process configured by default are Level 1 routers.
Command Modes
Router configuration
Command History
10.3 This command was introduced. 12.0(5)T This command was modified to include multiarea IS-IS routing.
Release
Modification
Usage Guidelines
It is highly recommended that you configure the type of an IS-IS routing process. If you are configuring multiarea IS-IS, you must configure the type of the router, or allow it to be configured by default. By default, the first instance of the IS-IS routing process that you configure using the router isis command is a Level 1-2 router.
If there is only one area in the network, there is no need to run both Level 1 and Level 2 routing algorithms. If IS-IS is used for Connectionless Network Service (CLNS) routing (and there is only one area), Level 1-only must be used everywhere. If IS-IS is used for IP routing only (and there is only one area), you can run Level 2-only everywhere. Areas you add after the Level 1-2 area exists are by default Level 1 areas.
If the router instance has been configured for Level 1-2 (the default for the first instance of the IS-IS routing process in a Cisco unit), you can remove Level 2 (interarea) routing for the area using the is-type command. You can also use the is-type command to configure Level 2 routing for an area, but it must be the only instance of the IS-IS routing process configured for Level 2 on the Cisco unit.
Examples
The following example specifies an area router:
router isis is-type level-2-only
Related Commands
Enables the IS-IS routing protocol and specifies an IS-IS process. show clns neighbor areas Displays information about IS-IS neighbors and the areas to which they belong.
Command
Description
To configure an Intermediate System-to-Intermediate System (IS-IS) network entity title (NET) for the routing process, use the net router configuration command. To remove a NET, use the no form of this command.
net network-entity-title
Syntax Description
network-entity-title NET that specifies the area address and the system ID for an IS-IS routing process. This argument can be either an address or a name.
Defaults
No NET is configured and the IS-IS process will not start. A NET is mandatory.
Command Modes
Router configuration
Command History
10.0 This command was introduced. 12.0(5)T This command was modified to include multiarea IS-IS routing.
Release
Modification
Usage Guidelines
Under most circumstances, one and only one NET must be configured.
A NET is a network service access point (NSAP) where the last byte is always zero. On a Cisco router running IS-IS, a NET can be 8 to 20 bytes. The last byte is always the n-selector and must be zero.
The six bytes directly in front of the n-selector are the system ID. The system ID length is a fixed size and cannot be changed. The system ID must be unique throughout each area (Level 1) and throughout the backbone (Level 2).
All bytes in front of the system ID are the area ID.
Even when IS-IS is used to perform IP routing only (no Connectionless Network Service (CLNS) routing enabled), a NET must still be configured to define the router system ID and area ID.
Multiple NETs per router are allowed, with a maximum of three. In rare circumstances, it is possible to configure two or three NETs. In such a case, the area this router is in will have three area addresses. There will still be only one area, but it will have more area addresses.
Configuring multiple NETs can be temporarily useful in the case of network reconfiguration where multiple areas are merged, or where one area is split into more areas. Multiple area addresses enable you to renumber an area individually as needed.
If you are configuring multiarea IS-IS, the area ID must be unique, but the system ID portion of the NET must be the same for all IS-IS routing process instances.
Examples
The following example configures a router with system ID 0000.0c11.1110 and area ID 47.0004.004d.0001:
router isis Pieinthesky net 47.0004.004d.0001.0001.0c11.1111.00
The following example shows three IS-IS routing processes with three areas configured. Each area has a unique identifier, but the system ID is the same for all areas.
clns routing ... interface Tunnel529 ip address 10.0.0.5 255.255.255.0 ip router isis BB clns router isis BB interface Ethernet1 ip address 10.1.1.5 255.255.255.0 ip router isis A3253-01 clns router isis A3253-01 ! interface Ethernet2 ip address 10.2.2.5 255.255.255.0 ip router isis A3253-02 clns router isis A3253-02 ... router isis BB ! Defaults to "is-type level-1-2" net 49.2222.0000.0000.0005.00 ! router isis A3253-01 net 49.0553.0001.0000.0000.0005.00 is-type level-1 ! router isis A3253-02 net 49.0553.0002.0000.0000.0005.00 is-type level-1
Related Commands
Configures the routing level for an instance of the IS-IS routing process. Enables the IS-IS routing protocol and specifies an IS-IS process.
Command
Description
To cause an Intermediate System-to-Intermediate System (IS-IS) Level 1-2 border router to stop advertising the Level 1 area prefix into the Level 2 backbone when full connectivity is lost between the border router, all adjacent Level 1 routers, and end hosts, use the partition avoidance router configuration command. This command displays the output from different areas as a string or additional white space. To disable this output format, use the no form of the command .
partition avoidance area-tag
Syntax Description
area-tag Required for multiarea IS-IS configuration. Optional for conventional IS-IS configuration. Required for multiarea IS-IS configuration. Meaningful name for a routing process. If it is not specified, a null tag is assumed and the process is referenced with a null tag. This name must be unique among all IP or Connectionless Network Service Protocol (CLNS) router processes for a given router.
Defaults
By default the partition avoidance command is disabled.
Command Modes
Router configuration
Command History
12.0(5)T This command was introduced.
Release
Modification
Usage Guidelines
When the partition avoidance command is enabled, a multiarea router withdraws a Level 1 area prefix from the Level 2 backbone when it no longer has any active adjacencies to that Level 1 area. This withdrawal prevents the Level 1 area from appearing to be partitioned within the Level 2 backbone.
In International Standards Organization (ISO) CLNS networks using a redundant topology, it is possible for an area to become "partitioned" when full connectivity is lost between a Level 1-2 border router, all adjacent Level 1 routers, and end hosts. In such a case, multiple Level 1-2 border routers advertise the Level 1 area prefix into the backbone area, even though any one router can reach only a subset of the end hosts in the Level 1 area.
When enabled, the partition avoidance command prevents this partitioning by causing the border router to stop advertising the Level 1 area prefix into the Level 2 backbone.
Other cases of connectivity loss within the Level 1 area itself are not detected or corrected by the border router, and this command will have no effect.
Examples
The following example causes the routing process Finance to stop advertising the prefix for the area named "area1" with the router no longer has any active adjacencies to area1.
router isis Finance partition avoidance area1
Related Commands
Configures the routing level for an instance of the IS-IS routing process. Enables the IS-IS routing protocol and specifies an IS-IS process.
Command
Description
To enable the Intermediate System-to-Intermediate System (IS-IS) routing protocol and to specify an IS-IS process, use the router isis global configuration command. To disable IS-IS routing, use the no form of this command.
router isis area-tag
Syntax Description
area-tag Required for multiarea IS-IS configuration. Optional for conventional IS-IS configuration. Meaningful name for a routing process. If it is not specified, a null tag is assumed and the process is referenced with a null tag. This name must be unique among all IP or Connectionless Network Service (CLNS) router processes for a given router.
Defaults
The router isis command is disabled.
Command Modes
Global configuration
Command History
10.0 This command was introduced. 12.0(5)T Multiarea functionality was added, changing the way the tag argument (now area-tag) is used.
Release
Modification
Usage Guidelines
This command is used to enable routing for an area. An appropriate network entity title (NET) must be configured to specify the area address of the area and system ID of the router. Routing must be enabled on one or more interfaces before adjacencies may be established and dynamic routing is possible.
If you have IS-IS running and at least one International Standards Organization Interior Gateway Routing Protocol (ISO-IGRP) process, the IS-IS process and the ISO-IGRP process cannot both be configured without an area tag. The null tag can be used by only one process. If you run ISO-IGRP and IS-IS, a null tag can be used for IS-IS, but not for ISO-IGRP at the same time. However, each area in an IS-IS multiarea configuration should have a nonnull area tag to facilitate identification of the area.
You can configure only one IS-IS routing process to perform Level 2 (interarea) routing. You can configure this process to perform Level 1 (intra-area) routing at the same time. You can configure up to 29 additional processes as Level 1-only processes. If Level 2 routing is configured on any process, all additional processes are automatically configured as Level 1.
An interface cannot be part of more than one area, except in the case where the associated routing process is performing both Level 1 and Level 2 routing. On media (such as WAN media, for example) where subinterfaces are supported, different subinterfaces could be configured for different areas.
If Level 2 routing is not desired for a given area, use the is-type command to remove Level 2. Level 2 routing can then be enabled on some other router instance.
Explicit redistribution between IS-IS instances is prohibited (prevented by the parser). In other words, you cannot issue a redistribute isis tag command in the context of another IS-IS router instance (router isis area-tag). Redistribution from any other routing protocol into a particular area is possible, and is configured per router instance, as in Release 12.0 of the Cisco IOS software, using the redistribute and route map commands. By default, redistribution is into Level 2.
If multiple Level 1 areas are defined, the Target Address Resolution Protocol (TARP) behaves in the following way:
Examples
The following example configures IS-IS for IP routing, with system ID 0000.0000.0002 and area ID 01.0001, and enables IS-IS to form adjacencies on Ethernet 0 and serial 0 interfaces. The IP prefix assigned to Ethernet 0 will be advertised to other IS-IS routers:
router isis net 01.0001.0000.0000.0002.00 is-type level-1 ! interface ethernet 0 ip address 10.1.1.1 255.255.255.0 ip router isis ! interface serial 0 ip unnumbered ethernet0 ip router isis
The following example starts IS-IS routing with the optional area-tag argument, where Pieinthesky is the value for the area-tag argument:
router isis Pieinthesky
The following example specifies IS-IS as an IP routing protocol for a process named Finance, and specifies that the Finance process will be routed on interfaces Ethernet 0 and serial 0:
router isis Finance net 49.0001.aaaa.aaaa.aaaa.00 interface Ethernet 0 ip router isis Finance interface serial 0 ip router isis Finance
Related Commands
clns router isis Enables IS-IS routing for ISO CLNS on an interface and attaches an area designator to the routing process. Configures an IS-IS routing process for IP on an interface and attaches an area designator to the routing process. Configures an IS-IS NET for the routing process.
Command
Description
To configure the router to signal other routers not to use it as an intermediate hop in their shortest path first (SPF) calculations, use the set-overload-bit router configuration command. To remove the designation, use the no form of this command.
set-overload-bitSyntax Description
This command has no arguments or keywords.
Defaults
The overload bit is not set.
Command Modes
Router configuration
Command History
11.2 This command was introduced.
Release
Modification
Usage Guidelines
This command forces the router to set the overload bit (also known as the hippity bit) in its nonpseudonode link-state packets. Normally the setting of the overload bit is allowed only when a router runs into problems. For example, when a router is experiencing a memory shortage, it might be that the Link State database is not complete, resulting in an incomplete or inaccurate routing table. By setting the overload bit in its LSPs, other routers can ignore the unreliable router in their SPF calculations until the router has recovered from its problems.
The result will be that no paths through this router are seen by other routers in the IS-IS area. However, IP and CLNS prefixes directly connected to this router will be still be reachable.
This command can be useful when you want to connect a router to an ISIS network, but do not want real traffic flowing through it under any circumstances. Examples are:
Examples
The following example configures the set-overload bit:
router isis set-overload-bit
To display the Intermediate System-to-Intermediate System (IS-IS) link state database, use the show isis database EXEC command.
show isis area-tag database [level-1] [level-2] [l1] [l2] [detail] [lspid]
Syntax Description
area-tag Required for multiarea IS-IS configuration. Optional for conventional IS-IS configuration. Meaningful name for a routing process. This name must be unique among all IP or Connectionless Network Service (CLNS) router processes for a given router. If an area tag is not specified, a null tag is assumed and the process is referenced with a null tag. If an area tag is specified, output is limited to the specified area. level-1 (Optional) Displays the IS-IS link state database for Level 1. level-2 (Optional) Displays the IS-IS link state database for Level 2. l1 (Optional) Abbreviation for the option level-1. l2 (Optional) Abbreviation for the option level-2. detail (Optional) When specified, the contents of each LSP are displayed. Otherwise, a summary display is provided. lspid (Optional) Link-state PDU identifier. When specified, the contents of a single LSP is displayed by its ID number.
Command Modes
EXEC
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
Each of the options shown in brackets for this command can be entered in an arbitrary string within the same command entry. For example, the following are both valid command specifications and provide the same output: show isis database detail l2 and show isis database l2 detail.
Examples
The following is sample output from the show isis database command when it is specified with no options or as show isis database l1 l2:
Router# show isis database IS-IS Level-1 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 0000.0C00.0C35.00-00 0x0000000C 0x5696 792 0/0/0 0000.0C00.40AF.00-00* 0x00000009 0x8452 1077 1/0/0 0000.0C00.62E6.00-00 0x0000000A 0x38E7 383 0/0/0 0000.0C00.62E6.03-00 0x00000006 0x82BC 384 0/0/0 0800.2B16.24EA.00-00 0x00001D9F 0x8864 1188 1/0/0 0800.2B16.24EA.01-00 0x00001E36 0x0935 1198 1/0/0 IS-IS Level-2 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 0000.0C00.0C35.03-00 0x00000005 0x04C8 792 0/0/0 0000.0C00.3E51.00-00 0x00000007 0xAF96 758 0/0/0 0000.0C00.40AF.00-00* 0x0000000A 0x3AA9 1077 0/0/0
Table 63 describes significant fields shown in the display
.
| Field | Description |
|---|---|
LSPID | The LSP identifier. The first six octets form the System ID of the router that originated the LSP. |
LSP Seq Num | Sequence number for the LSP that allows other systems to determine if they have received the latest information from the source. |
LSP Checksum | Checksum of the entire LSP packet. |
LSP Holdtime | Amount of time the LSP remains valid, in seconds. An LSP holdtime of zero indicates that this LSP was purged and is being removed from all routers' LSDB. The value between brackets indicates how long the purged LSP will stay in the LSDB before being completely removed. |
ATT | The Attach bit. This indicates that the router is also a Level 2 router, and it can reach other areas. Level 1-only routers and Level 1-2 routers that have lost connection to other Level 2 routers will use the attached bit to find the closest Level 2 router. They will point a default route to the closest Level 2 router. |
P | The P bit. Detects if the IS is area partition repair capable. Cisco and other vendors do not support area partition repair. |
OL | The Overload bit. Determines if the IS is congested. If the Overload bit is set, other routers will not use this system as a transit router when calculating routers. Only packets for destinations directly connected to the overloaded router will be sent to this router. |
Example Using Show IS-IS Database Detail
The following is sample output from the show isis database detail command.
Router# show isis database detail IS-IS Level-1 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 0000.0C00.0C35.00-00 0x0000000C 0x5696 325 0/0/0 Area Address: 47.0004.004D.0001 Area Address: 39.0001 Metric: 10 IS 0000.0C00.62E6.03 Metric: 0 ES 0000.0C00.0C35 --More-- 0000.0C00.40AF.00-00* 0x00000009 0x8452 608 1/0/0 Area Address: 47.0004.004D.0001 Metric: 10 IS 0800.2B16.24EA.01 Metric: 10 IS 0000.0C00.62E6.03 Metric: 0 ES 0000.0C00.40AF IS-IS Level-2 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 0000.0C00.0C35.03-00 0x00000005 0x04C8 317 0/0/0 Metric: 0 IS 0000.0C00.0C35.00 --More-- 0000.0C00.3E51.00-00 0x00000009 0xAB98 1182 0/0/0 Area Address: 39.0004 Metric: 10 IS 0000.0C00.40AF.00 Metric: 10 IS 0000.0C00.3E51.05
As the output shows, in addition to the information displayed with show isis database, the show isis database detail command displays the contents of each LSP.
Table 64 describes the additional fields shown in the display.
.
| Field | Description |
|---|---|
Area Address: | Reachable area addresses from the router. For Level 1 LSPs, these are the area addresses configured manually on the originating router. For Level 2 LSPs, these are all the area addresses for the area this route belongs to. |
Metric: | IS-IS metric for the cost of the adjacency between the originating router and the advertised neighbor, or the metric of the cost to get from the advertising router to the advertised destination (which can be an IP address, an ES or a CLNS prefix). |
Example Using Show IS-IS Database Detail Displaying IP Addresses
The following is additional sample output from the show isis database detail command.This is a Level 2 LSP. The area address 39.0001 is the address of the area in which the router resides.
Router# show isis database detail l2 IS-IS Level-2 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 0000.0C00.1111.00-00* 0x00000006 0x4DB3 1194 0/0/0 Area Address: 39.0001 NLPID: 0x81 0xCC IP Address: 160.89.64.17 Metric: 10 IS 0000.0C00.1111.09 Metric: 10 IS 0000.0C00.1111.08 Metric: 10 IP 160.89.65.0 255.255.255.0 Metric: 10 IP 160.89.64.0 255.255.255.0 Metric: 0 IP-External 10.0.0.0 255.0.0.0
Table 65 describes the additional field shown in the display.
| Field | Description |
|---|---|
Various addresses | The "IP" entries are the directly connected IP subnets the router is advertising (with associated metrics). The "IP-External" is a redistribute route. |
To display how often and why the router has run a full shortest path first (SPF) calculation, use the show isis spf-log user EXEC command.
show isis area-tag spf-log
Syntax Description
area-tag Required for multiarea IS-IS configuration. Optional for conventional IS-IS configuration. Meaningful name for a routing process. This name must be unique among all IP or Connectionless Network Service (CLNS) router processes for a given router. If an area tag is not specified, a null tag is assumed and the process is referenced with a null tag. If an area tag is specified, output is limited to the specified area.
Command Modes
User EXEC
Command History
10.0 This command was introduced.
Release
Modification
Examples
The following is sample output from the show isis spf-log command:
Router# show isis spf-log
Level 1 SPF log
When Duration Nodes Count Last trigger LSP Triggers
00:15:46 3124 40 1 milles.00-00 TLVCODE
00:15:24 3216 41 5 milles.00-00 TLVCODE NEWLSP
00:15:19 3096 41 1 deurze.00-00 TLVCODE
00:14:54 3004 41 2 milles.00-00 ATTACHFLAG LSPHEADER
00:14:49 3384 41 1 milles.00-01 TLVCODE
00:14:23 2932 41 3 milles.00-00 TLVCODE
00:05:18 3140 41 1 PERIODIC
00:03:54 3144 41 1 milles.01-00 TLVCODE
00:03:49 2908 41 1 milles.01-00 TLVCODE
00:03:28 3148 41 3 bakel.00-00 TLVCODE TLVCONTENT
00:03:15 3054 41 1 milles.00-00 TLVCODE
00:02:53 2958 41 1 mortel.00-00 TLVCODE
00:02:48 3632 41 2 milles.00-00 NEWADJ TLVCODE
00:02:23 2988 41 1 milles.00-01 TLVCODE
00:02:18 3016 41 1 gemert.00-00 TLVCODE
00:02:14 2932 41 1 bakel.00-00 TLVCONTENT
00:02:09 2988 41 2 bakel.00-00 TLVCONTENT
00:01:54 3228 41 1 milles.00-00 TLVCODE
00:01:38 3120 41 3 rips.03-00 TLVCONTENT
Table 66 describes the fields in the display.
| Field | Description |
|---|---|
When | How long ago (hh:mm:ss) a full SPF calculation occurred. The last 20 occurrences are logged. |
Duration | Number of milliseconds it took to complete this SPF run. Elapsed time is wall clock time, not CPU time. |
Nodes | Number of routers and pseudonodes (LANs) that make up the topology calculated in this SPF run. |
Count | Number of events that triggered this SPF run. When there is a topology change, often multiple LSPs are received in a short time. A router waits 5 seconds before running a full SPF run, so it can include all new information. This count denotes the number of events (such as receiving new LSPs) that occurred while the router was waiting its 5 seconds before running full SPF. |
Last trigger LSP | Whenever a full SPF calculation is triggered by the arrival of a new LSP, the router stores the LSP id. The LSP id can give a clue as to the source of routing instability in an area. If multiple LSPs are causing an SPF run, only the LSP id of the last received LSP is remembered. |
Triggers | A list of all reasons that triggered a full SPF calculation. For a list of possible triggers, see Table 67. |
Table 67 gives a list of possible triggers of a full SPF calculation.
| Trigger | Description |
|---|---|
PERIODIC | Typically, every 15 minutes a router runs a periodic full SPF calculation. |
NEWSYSID | A new system ID (via NET) was configured on this router. |
NEWAREA | A new area (via NET) was configured on this router. |
NEWLEVEL | A new level (via is-type) was configured on this router. |
RTCLEARED | A clear clns route command was issued on this router. |
NEWMETRIC | A new metric was configured on an interface of this router. |
IPBACKUP | An IP route disappeared, which was not learned via IS-IS, but via another protocol with better administrative distance. IS-IS will run a full SPF to install an IS-IS route for the disappeared IP prefix. |
IPQUERY | A clear ip route command was issued on this router. |
ATTACHFLAG | This router is now attached to the L2 backbone or it has just lost contact to the L2 backbone. |
ADMINDIST | Another administrative distance was configured for the IS-IS process on this router. |
AREASET | Set of learned area-addresses in this area changed. |
NEWADJ | This router has created a new adjacency to another router. |
DBCHANGED | A clear isis * command was issued on this router. |
BACKUPOVFL | An IP prefix disappeared. The router knows there is another way to reach that prefix, but has not stored that backup route. The only way to find the alternative route is to run a full SPF run. |
NEWLSP | A new router or pseudonode appeared in the topology. |
LSPEXPIRED | Some LSP in the LSDB has expired. |
LSPHEADER | ATT/P/OL bits or is-type in an LSP header changed. |
TLVCODE | TLV code mismatch, indicating that different TLVs are included in the newest version of an LSP. |
TLVCONTENT | TLV contents changed. This normally indicates that an adjacency somewhere in the area has come up or gone down. Look at the "Last trigger LSP" to get an indication of where the instability may have occurred. |
To display a list of all connected routers in all areas, use the show isis topology EXEC command.
show isis area-tag topology
Syntax Description
area-tag Required for multiarea IS-IS configuration. Optional for conventional IS-IS configuration. Meaningful name for a routing process. This name must be unique among all IP or Connectionless Network Service (CLNS) router processes for a given router. If an area tag is not specified, a null tag is assumed and the process is referenced with a null tag. If an area tag is specified, output is limited to the specified area.
Command Modes
EXEC
Command History
12.0(5)T This command was introduced.
Release
Modification
Usage Guidelines
Use the show isis topology EXEC command to verify the presence and connectivity between all routers in all areas.
Examples
The following example shows output from the show isis topology command in a dual CLNS-IP network:
dtp-5# show isis topology Area L2BB: IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA 0000.0000.0005 -- 0000.0000.0009 10 0000.0000.0009 Tu529 *Tunnel* 0000.0000.0017 20 0000.0000.0009 Tu529 *Tunnel* 0000.0000.0053 30 0000.0000.0009 Tu529 *Tunnel* 0000.0000.0068 20 0000.0000.0009 Tu529 *Tunnel* IS-IS paths to level-2 routers System Id Metric Next-Hop Interface SNPA 0000.0000.0005 -- 0000.0000.0009 10 0000.0000.0009 Tu529 *Tunnel* 0000.0000.0017 20 0000.0000.0009 Tu529 *Tunnel* 0000.0000.0053 30 0000.0000.0009 Tu529 *Tunnel* 0000.0000.0068 20 0000.0000.0009 Tu529 *Tunnel* Area A3253-01: IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA 0000.0000.0003 10 0000.0000.0003 Et1 0000.0c03.6944 0000.0000.0005 -- 0000.0000.0053 10 0000.0000.0053 Et1 0060.3e58.ccdb Area A3253-02: IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA 0000.0000.0002 10 0000.0000.0002 Et2 0000.0c03.6bc5 0000.0000.0005 -- 0000.0000.0053 10 0000.0000.0053 Et2 0060.3e58.ccde
Related Commands
show clns es-neighbors Lists the ES neighbors that this router knows. show clns is-neighbors Displays IS-IS related information for IS-IS router adjacencies. show clns neighbor areas Displays information about IS-IS neighbors and the areas to which they belong. show clns route Displays one or all of the destinations to which the router knows how to route CLNS packets. show clns neighbors Displays both ES and IS neighbors.
Command
Description
To create aggregate addresses for Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF), use the summary-address router configuration command. Use the no form of the command to restore the default.
summary-address address mask {level-1 | level-1-2 | level-2} prefix mask
Syntax Description
address Summary address designated for a range of addresses. mask IP subnet mask used for the summary route. level-1 Only routes redistributed into Level 1 are summarized with the configured address/mask value. level-1-2 The summary router will be applied both when redistributing routes into Level 1 and Level 2 IS-IS, and when L2 IS-IS advertised Level 1 routes reachable in its area. level-2 Routes learned by Level 1 routing will be summarized into the Level 2 backbone with the configured address/mask value, and redistributed routes into Level 2 IS-IS will be summarized also. prefix IP route prefix for the destination. mask IP subnet mask used for the summary route.
Defaults
All redistributed routes are advertised individually.
Command Modes
Router configuration
Command History
10.0 This command was introduced.
Release
Modification
Usage Guidelines
This command also reduces the size of the link-state packets (LSPs) and thus the link-state Database. It also helps stability because a summary advertisement is depending on many more specific routes. If one more specific route flaps, in most cases this does not cause a flap of the summary advertisement.
The drawback of summary addresses is that other routes might have less information to calculate the most optimal routing table for all individual destinations.
Examples
The following example redistributes Routing Information Protocol (RIP) routes into IS-IS. In the RIP world, there are IP routes for 10.1.1, 10.1.2, 10.1.3, 10.1.4, and so forth. This example advertises only 10.1.0.0 into our IS-IS Level 1 Link State PDU.
router isis net 01.0000.0000.0001.00 redistribute rip level-1 metric 40 summary-address 10.1.0.0 255.255.0.0 level-1
Posted: Thu Jul 27 13:23:54 PDT 2000
Copyright 1989-2000©Cisco Systems Inc.