- IS-IS Overview and Basic Configuration
- Reducing Failure Detection Times in IS-IS Networks
- Enhancing Security in an IS-IS Network
- Configuring Integrated IS-IS Protocol Shutdown Support Maintaining Configuration Parameters
- IS-IS Support for Route Tags
- IS-IS Multiarea Support
- IS-IS Support for an IS-IS Instance per VRF for IP
- IPv6 Routing: IS-IS Multitopology Support for IPv6
- IPv6 Routing: IS-IS Support for IPv6
- IPv6 Routing: Route Redistribution
- Finding Feature Information
- Prerequisites for IS-IS Support for Route Tags
- Information About IS-IS Support for Route Tags
IS-IS Support for Route Tags
The IS-IS Support for Route Tags feature enables you to tag Intermediate System-to-Intermediate System (IS-IS) route prefixes and use those tags in a route map to control IS-IS route redistribution or route leaking. The results are network scalability and faster convergence for device updates.
- Finding Feature Information
- Prerequisites for IS-IS Support for Route Tags
- Information About IS-IS Support for Route Tags
- How to Configure IS-IS Support for Route Tags
- Configuration Examples for IS-IS Support for Route Tags
- Where to Go Next
- Additional References
- Feature Information for IS-IS Support for Route Tags
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for IS-IS Support for Route Tags
Because the Intermediate System-to-Intermediate System (IS-IS) route tag will be used in a route map, you must understand how to configure a route map.
To use the route tag, you must configure the metric-style wide command. (The metric-style narrow command is configured by default.) The tag value is set into sub-TLV 1 for type, length, values (TLV) Type 135.
You must understand the task for which you are using the route tag, such as route redistribution, route summarization, or route leaking.
You should be familiar with the concepts described in the “Overview of IS-IS Fast Convergence” module.
Before you tag any IS-IS routes, you need to make the following decisions:
Information About IS-IS Support for Route Tags
Route Redistribution
Devices are allowed to redistribute external prefixes, or routes, that are learned from any other routing protocol, static configuration, or connected interfaces. The redistributed routes are allowed in either a Level 1 device or a Level 2 device. Level 2 routes injected as Level 1 routes is called route leaking.
IS-IS Routes Tagged to Control Their Redistribution
You can control the redistribution of Intermediate System-to-Intermediate System (IS-IS) routes by tagging them. The term “route leaking” refers to controlling distribution through tagging of routes.
- How Route Summarization Can Enhance Scalability in IS-IS Networks
- Benefits of IS-IS Route Tags
- IS-IS Route Tag Characteristics
- IS-IS Route Leaking Based on a Route Tag
How Route Summarization Can Enhance Scalability in IS-IS Networks
Summarization is a key factor that enhances the scalability of a routing protocol. Summarization reduces the number of routing updates that are flooded across areas or routing domains. For example, in multiarea Intermediate System-to-Intermediate System (IS-IS) networks, a good addressing scheme can optimize summarization by not allowing an overly large Level 2 database to be unnecessarily populated with updates that have come from Level 1 areas.
A device can summarize prefixes on redistribution whether the prefixes have come from internal prefixes, local redistribution, or Level 1 device redistribution. Routes that have been leaked from Level 2 to Level 1 and routes that are advertised into Level 2 from Level 1 can also be summarized.
Benefits of IS-IS Route Tags
The IS-IS Support for Route Tags feature allows you to tag IP addresses of an interface and use the tag to apply administrative policy with a route map.
You can tag Intermediate System-to-Intermediate System (IS-IS) routes to control their redistribution. You can configure a route map to set a tag for an IS-IS IP prefix (route) or match on the tag (perhaps on a different device) to redistribute IS-IS routes. Although the match tag and set tag commands existed for other protocols before the IS-IS Support for Route Tags feature, they were not implemented for IS-IS, so they did nothing when specified in an IS-IS network.
You can tag a summary route and then use a route map to match the tag and set one or more attributes for the route.
IS-IS Route Tag Characteristics
An Intermediate System-to-Intermediate System (IS-IS) route tag number can be up to 4 bytes long. The tag value is set into a sub-TLV 1 for type, length, values (TLV) Type 135.
Only one tag can be set to an IS-IS IP route (prefix). The tag is sent in link-state packet (LSP) protocol data units (PDUs) advertising the route. Setting a tag to a route alone does nothing for your network. You can use the route tag at area or Level 1/Level 2 boundaries by matching on the tag and then applying administrative policies such as redistribution, route summarization, or route leaking.
Configuring a tag for an interface (with the isis tag command) triggers the generation of new LSPs from the device because the tag is new information for the PDUs.
IS-IS Route Leaking Based on a Route Tag
You can tag Intermediate System-to-Intermediate System (IS-IS) routes to configure route leaking (redistribution). Because only the appropriate routes are redistributed—or leaked—the results is network scalability and faster convergence for the device update. If you configure route leaking and you want to match on a tag, use a route map (not a distribute list).
There are two general steps to using IS-IS route tags: tagging routes and referencing the tag to set values for the routes or redistribute routes.
There are three ways to tag IS-IS routes: tag routes for networks directly connected to an interface, set a tag in a route map, or tag a summary route. The tagging method is independent of how you use the tag.
After you tag the routes, you can use the tag to set values (such as metric, next hop, and so on) or redistribute routes. You might tag routes on one device, but reference the tag on other devices, depending on what you want to achieve. For example, you could tag the interface on Device A with a tag, match the tag on Device B to set values, and redistribute routes on Device C based on values using a route map.
How to Configure IS-IS Support for Route Tags
- Tagging Routes for Networks Directly Connected to an Interface
- Tagging Routes Using a Route Map
- Tagging a Summary Address
- Using the Tag to Set Values or Redistribute Routes
- Monitoring IS-IS Network Convergence Time
Tagging Routes for Networks Directly Connected to an Interface
1.
enable
2.
configure terminal
3.
interface
type number
4.
ip address
ip-address mask
5.
ip address
ip-address mask
secondary
6.
isis tag
tag-number
7.
end
8.
show isis database verbose
9.
show ip route [ip-address [mask] [longer-prefixes] |
protocol [process-id] |
list [access-list-number |
access-list-name]]
DETAILED STEPS
What to Do Next
Applying the tag does nothing of value for your network until you use the tag by referencing it in a route map, either to set values, to redistribute routes, or to do both. Proceed to the section “Using the Tag to Set Values or Redistribute Routes.”
Tagging Routes Using a Route Map
1.
enable
2.
configure terminal
3.
route-map
map-tag [permit |
deny] [sequence-number]
4.
match tag
tag-value [...tag-value]
5. Use an additional match command for each match criterion that you want.
6.
set tag
tag-value
7. Set another value, depending on what else you want to do with the tagged routes.
8. Repeat Step 7 for each value that you want to set.
9. Repeat Steps 3 through 8 for each route-map statement that you want.
10.
end
11.
show isis database verbose
12.
show ip route [ip-address [mask] [longer-prefixes] |
protocol [process-id] | [list [access-list-number |
access-list-name]]
DETAILED STEPS
What to Do Next
Applying the tag does nothing of value for your network until you use the tag by referencing it in a route map, either to set values, to redistribute routes, or to do both. Proceed to the section “Using the Tag to Set Values and or Redistribute Routes.”
Tagging a Summary Address
If a tagged route is summarized and the tag is not explicitly configured in the summary-address command, the tag is lost.
1.
enable
2.
configure terminal
3.
router isis [area-tag]
4.
metric-style wide
5.
summary-address
address mask [level-1 |
level-1-2 |
level-2] [tag
tag-number] [metric
metric-value]
6.
end
7.
show isis database verbose
8.
show ip route [ip-address [mask] [longer-prefixes] |
protocol [process-id] | [list [access-list-number |
access-list-name]]
DETAILED STEPS
What to Do Next
Applying the tag does nothing of value for your network until you use the tag by referencing it in a route map to set values. It is unlikely that you will redistribute summary routes. Proceed to the “Using the Tag to Set Values or Redistribute Routes” section.
Using the Tag to Set Values or Redistribute Routes
You must have already applied a tag on the interface, in a route map, or on a summary route. See the section “Tagging IS-IS Routes to Control Their Distribution.”
1.
enable
2.
configure terminal
3.
route-map
map-tag [permit |
deny] [sequence-number]
4.
match tag
tag-value
5. Specify a match command for each match criterion that you want.
6. Set a value, depending on what you want to do with the tagged routes.
7. Repeat Step 6 for each value that you want to set.
8. Repeat Steps 3 through 7 for each route-map statement that you want.
9.
exit
10.
router isis
11.
metric-style wide
12.
redistribute
protocol [process-id] {level-1 |
level-1-2 |
level-2} [metric
metric-value] [metric-type
type-value] [route-map
map-tag]
DETAILED STEPS
Monitoring IS-IS Network Convergence Time
1.
enable
2.
configure
terminal
3.
isis display
delimiter [return
count
|
character
count]
4.
exit
5.
show isis
database [level-1] [level-2] [l1] [l2] [detail] [lspid]
6.
show
isis [area-tag]
route
7.
show
isis [area-tag] [ipv6 |
*]
spf-log
8.
show
isis [process-tag]
topology
DETAILED STEPS
Examples
The following sample output from the show isis spf-log command displays this information:
-
When the SPFs were executed
-
Total elapsed time for the SPF computation
-
Number of nodes that make up the topology in the SPF calculation
-
Number of triggers that caused the SPF calculation
-
Information regarding what triggered the SPF calculation
Device# 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
Configuration Examples for IS-IS Support for Route Tags
- Example: Tagging Routes for Networks Directly Connected to an Interface and Redistributing Them
- Example: Redistributing IS-IS Routes Using a Route Map
- Example: Tagging a Summary Address and Applying a Route Map
- Example: Redistributing IS-IS Routes Using an Access List and a Route Map
Example: Tagging Routes for Networks Directly Connected to an Interface and Redistributing Them
In this example, two interfaces are tagged with different tag values. By default, these two IP addresses would have been put into the Intermediate System-to-Intermediate System (IS-IS) Level 1 and Level 2 database. However, by using the redistribute command with a route map to match tag 110, only IP address 172.16.10.5 255.255.255.0 is put into the Level 2 database.
interface Gigabitethernet 1/0/0 ip address 192.168.129.1 255.255.255.0 ip router isis isis tag 120 interface Gigabitethernet 1/1/0 ip address 172.16.10.5 255.255.255.0 ip router isis isis tag 110 router isis net 49.0001.0001.0001.0001.00 redistribute isis ip level-1 into level-2 route-map match-tag route-map match-tag permit 10 match tag 110
Example: Redistributing IS-IS Routes Using a Route Map
In a scenario using route tags, you might configure some commands on one device and other commands on another device. For example, you might have a route map that matches on a tag and sets a different tag on a device at the edge of a network, and on different devices you might configure the redistribution of routes based on a tag in a different route map.
The figure below illustrates a flat Level 2 Intermediate System-to-Intermediate System (IS-IS) area. On the left edge are static routes from Device A to reach some IP prefixes. Device A redistributes the static routes into IS-IS. Device B runs the Border Gateway Protocol (BGP) and redistributes IS-IS routes into BGP and then uses the tag to apply different administrative policy based on different tag values.
Device A
router isis net 49.0000.0000.0001.00 metric-style wide redistribute static ip route-map set-tag ! route-map set-tag permit 5 set tag 10
Device B
router bgp 100 redistribute isis level-2 route-map tag-policy route-map tag-policy permit 20 match tag 10 set metric 1000
Example: Tagging a Summary Address and Applying a Route Map
The figure below illustrates two Level 1 areas and one Level 2 area between them. Device A and Device B are Level 1/Level 2 edge devices in the Level 2 area. On edge Device A, a summary address is configured to reduce the number of IP addresses put into the Level 2 Intermediate System-to-Intermediate System (IS-IS) database. Also, a tag value of 100 is set to the summary address.
On Device B, the summary address is leaked into the Level 1 area, and administrative policy is applied based on the tag value.
Device A
router isis net 49.0001.0001.0001.00 metric-style wide summary-address 10.0.0.0 255.0.0.0 tag 100
Device B
router isis net 49.0002.0002.0002.0002.0 metric-style wide redistribute isis ip level-2 into level-1 route-map match-tag route-map match-tag permit 10 match tag 100
Example: Redistributing IS-IS Routes Using an Access List and a Route Map
In this example, the first redistribute isis ip command controls the redistribution of Level 1 routes into Level 2. Only the routes with the tag of 90 and whose IP prefix is not 192.168.130.5/24 are redistributed from Level 1 into Level 2.
The second redistribute isis ip command controls the route leaking from Level 2 into the Level 1 domain. Only the routes tagged with 60 or 50 are redistributed from Level 2 into Level 1.
interface Gigabitethernet 1/0/0 ip address 192.168.130.5 255.255.255.0 ip router isis isis tag 60 ! interface Gigabitethernet 2/0/0 ip address 192.168.130.15 255.255.255.0 ip router isis isis tag 90 ! interface Gigabitethernet 3/0/0 ip address 192.168.130.25 5 255.255.255.0 ip router isis isis tag 50 ! router isis net 49.0001.0001.0001.0001.00 metric-style wide redistribute isis ip level-1 into level-2 route-map redist1-2 redistribute isis ip level-2 into level-1 route-map leak2-1 ! access-list 102 deny ip host 192.168.130.5 host 255.255.255.255 access-list 102 permit ip any any ! route-map leak2-1 permit 10 match tag 60 ! route-map leak2-1 permit 20 match tag 50 ! route-map redist1-2 permit 10 match ip address 102 match tag 90
Where to Go Next
To configure features to improve Intermediate System-to-Intermediate System (IS-IS) network convergence times, complete the optional tasks in one or more of the following modules in the IP Routing: IS-IS Configuration Guide:
Additional References
Related Documents
Technical Assistance
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Link |
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Feature Information for IS-IS Support for Route Tags
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to . An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
---|---|---|
IS-IS Support for Route Tags |
Cisco IOS XE Release 3.1.0SG Cisco IOS XE Release 3.6E |
The IS-IS Support for Route Tags feature enables you to tag Intermediate System-to-Intermediate System (IS-IS) route prefixes and use those tags in a route map to control IS-IS route redistribution or route leaking. The following commands were introduced or modified: isis tag, match tag, metric-style wide, router isis, route-map, set tag, show ip route, show isis database verbose, summary-address. In Cisco IOS XE Release 3.6E, this feature is supported on Cisco Catalyst 3850 Series Switches |