ISIS route aggregation

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Let’s keep going and try to configure ISIS route aggregation based on the following topology:

ISIS route aggregation on Huawei routers topology

If you want to recall how to configure ISIS adjacency on Huawei routers, just go to ‘ISIS on Huawei routers‘.

To avoid DIS election, configure all physical interfaces as ISIS point-to-point (p2p) links (Router 1 as an example):

[1-Ethernet0/0/8]isis circuit-type p2p

[1]dis isis interface 

                       Interface information for ISIS(1)
                       ---------------------------------
 Interface       Id      IPV4.State          IPV6.State      MTU  Type  DIS   
 Eth0/0/8        003         Up                 Down         1497 L1/L2 -- 
 Loop0           001         Up                 Down         1500 L1/L2 -- 
 Loop100         002         Up                 Down         1500 L1/L2 -- 

[1]dis isis interface Ethernet 0/0/8 verbose 

                       Interface information for ISIS(1)
                       ---------------------------------
 Interface       Id      IPV4.State          IPV6.State      MTU  Type  DIS   
 Eth0/0/8        003         Up                 Down         1497 L1/L2 -- 
  Circuit MT State            : Standard 
  Circuit Parameters          : p2p 
  Description                 : HUAWEI, AR Series, Ethernet0/0/8 Interface
  SNPA Address                : 00e0-fc03-993e
  IP Address                  : 10.0.1.1
  IPV6 Link Local Address     :
  IPV6 Global Address(es)     :
  Csnp Timer Value            :  L12   10
  Hello Timer Value           :        10
  DIS Hello Timer Value       :
  Hello Multiplier Value      :         3
  Cost                        :  L1    10  L2    10
  Ipv6 Cost                   :  L1    10  L2    10
  Retransmit Timer Value      :  L12    5
  LSP-Throttle Timer          :  L12   50
  Bandwidth-Value             :  Low  100000000  High          0
  Static Bfd                  :  NO
  Dynamic Bfd                 :  NO
  Fast-Sense Rpr              :  NO
  Extended-Circuit-Id Value   :  0000000003

What we want to do today are:

  • Configure Loopback100 interface on Router 1 and assign 10.0.100./32 IP address to it
  • Enable ISIS protocol on Loopback100
  • Configure three static routes: 10.0.2.0/24, 10.0.3.0/24, 10.0.4.0/24 on Router 1
  • Import the static routes to ISIS
  • Aggregate these networks on Level-1-2 router (router 2).

Let’s do it. Configure Loopback100 and enable ISIS on it:

[1]interface LoopBack 100
[1-LoopBack100]ip address 10.0.100.1 32
[1-LoopBack100]isis enable

Configure static routes on Router 1 to simulate networks that should be aggregated:

[1]ip route-static 10.0.2.0 255.255.255.0 NULL0
[1]ip route-static 10.0.3.0 255.255.255.0 NULL0
[1]ip route-static 10.0.4.0 255.255.255.0 NULL0

Import these three routes into ISIS:

[1]isis
[1-isis-1]import-route static level-1

Check the routing table of Router 1:

[1]dis ip rout
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
         Destinations : 16       Routes : 16       

Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface

        0.0.0.0/0   ISIS-L1 15   10          D   10.0.1.2        Ethernet0/0/8
        1.1.1.1/32  Direct  0    0           D   127.0.0.1       LoopBack0
        2.2.2.2/32  ISIS-L1 15   10          D   10.0.1.2        Ethernet0/0/8
       10.0.1.0/30  Direct  0    0           D   10.0.1.1        Ethernet0/0/8
       10.0.1.1/32  Direct  0    0           D   127.0.0.1       Ethernet0/0/8
       10.0.1.3/32  Direct  0    0           D   127.0.0.1       Ethernet0/0/8
       10.0.2.0/24  Static  60   0           D   0.0.0.0         NULL0
       10.0.3.0/24  Static  60   0           D   0.0.0.0         NULL0
       10.0.4.0/24  Static  60   0           D   0.0.0.0         NULL0
     10.0.100.1/32  Direct  0    0           D   127.0.0.1       LoopBack100
       20.0.0.0/30  ISIS-L1 15   20          D   10.0.1.2        Ethernet0/0/8
      127.0.0.0/8   Direct  0    0           D   127.0.0.1       InLoopBack0
      127.0.0.1/32  Direct  0    0           D   127.0.0.1       InLoopBack0
127.255.255.255/32  Direct  0    0           D   127.0.0.1       InLoopBack0
255.255.255.255/32  Direct  0    0           D   127.0.0.1       InLoopBack0

Check the routing table of Router 5 to find how our networks have been advertised:

[5]dis ip routing-table 
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
         Destinations : 17       Routes : 17       

Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface

        1.1.1.1/32  ISIS-L2 15   30          D   40.0.0.1        Ethernet0/0/8
        2.2.2.2/32  ISIS-L2 15   20          D   40.0.0.1        Ethernet0/0/8
        4.4.4.4/32  ISIS-L2 15   10          D   40.0.0.1        Ethernet0/0/8
        5.5.5.5/32  Direct  0    0           D   127.0.0.1       LoopBack0
       10.0.1.0/30  ISIS-L2 15   30          D   40.0.0.1        Ethernet0/0/8
       10.0.2.0/24  ISIS-L2 15   94          D   40.0.0.1        Ethernet0/0/8
       10.0.3.0/24  ISIS-L2 15   94          D   40.0.0.1        Ethernet0/0/8
       10.0.4.0/24  ISIS-L2 15   94          D   40.0.0.1        Ethernet0/0/8
     10.0.100.1/32  ISIS-L2 15   30          D   40.0.0.1        Ethernet0/0/8
       20.0.0.0/30  ISIS-L2 15   20          D   40.0.0.1        Ethernet0/0/8
       40.0.0.0/30  Direct  0    0           D   40.0.0.2        Ethernet0/0/8
       40.0.0.2/32  Direct  0    0           D   127.0.0.1       Ethernet0/0/8
       40.0.0.3/32  Direct  0    0           D   127.0.0.1       Ethernet0/0/8
      127.0.0.0/8   Direct  0    0           D   127.0.0.1       InLoopBack0
      127.0.0.1/32  Direct  0    0           D   127.0.0.1       InLoopBack0
127.255.255.255/32  Direct  0    0           D   127.0.0.1       InLoopBack0
255.255.255.255/32  Direct  0    0           D   127.0.0.1       InLoopBack0

These three static routes configured on Router 1 are imported into ISIS and we can find them in the routing table of Router 5. It should be noted that ISIS has no external routes, unlike OSPF. The origin of the routes is still ISIS, with preference 15. As you can see, the IP address of Loopback100 of Router 1 is also found in the routing table of Router 5.

Let’s finally configure route aggregation. Based on the topology and networks configured, we can aggregate the following networks on Router 2:

  • 10.0.1.0/30
  • 10.0.2.0/24
  • 10.0.3.0/24
  • 10.0.4.0/24
  • 10.0.100.1/32.
[2]isis
[2-isis-1]summary 10.0.0.0 255.255.0.0 (Level-2 by default)

Verify the IP routing table of Router 5 once again:

[5]dis ip routing-table 
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
         Destinations : 13       Routes : 13       

Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface

        1.1.1.1/32  ISIS-L2 15   30          D   40.0.0.1        Ethernet0/0/8
        2.2.2.2/32  ISIS-L2 15   20          D   40.0.0.1        Ethernet0/0/8
        4.4.4.4/32  ISIS-L2 15   10          D   40.0.0.1        Ethernet0/0/8
        5.5.5.5/32  Direct  0    0           D   127.0.0.1       LoopBack0
       10.0.0.0/16  ISIS-L2 15   30          D   40.0.0.1        Ethernet0/0/8
       20.0.0.0/30  ISIS-L2 15   20          D   40.0.0.1        Ethernet0/0/8
       40.0.0.0/30  Direct  0    0           D   40.0.0.2        Ethernet0/0/8
       40.0.0.2/32  Direct  0    0           D   127.0.0.1       Ethernet0/0/8
       40.0.0.3/32  Direct  0    0           D   127.0.0.1       Ethernet0/0/8
      127.0.0.0/8   Direct  0    0           D   127.0.0.1       InLoopBack0
      127.0.0.1/32  Direct  0    0           D   127.0.0.1       InLoopBack0
127.255.255.255/32  Direct  0    0           D   127.0.0.1       InLoopBack0
255.255.255.255/32  Direct  0    0           D   127.0.0.1       InLoopBack0

Thus the routing table has been reduced.

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