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BGP route is not installed in ip routing table

Publication Date:  2018-03-01 Views:  109 Downloads:  0
Issue Description

Network Topology: Router 1 <---> Router 2   


The customer has established IBGP peer between two NE20E routers Router 1 and Router 2 for test. On Router 1, LoopBack5 and LoopBack10 interfaces are configured and their /32 routes are imported into BGP routing-table by “network” commands:

Router 1:

#

interface LoopBack5

 ip address 192.168.223.100 255.255.255.255

#

interface LoopBack10

 ip address 10.1.1.1 255.255.255.255

#

bgp 65534

 router-id 192.168.223.2

 peer 192.168.223.3 as-number 65534

 #

 ipv4-family unicast

  undo synchronization

  network 10.1.1.1 255.255.255.255

  network 192.168.223.100 255.255.255.255

  supernet unicast advertise enable

  peer 192.168.223.3 enable



Router 2:

#

bgp 65534

 router-id 192.168.223.3

 peer 192.168.223.2 as-number 65534

 #

 ipv4-family unicast

  undo synchronization

  supernet unicast advertise enable

  peer 192.168.223.2 enable

  peer 192.168.223.2 keep-all-routes

 #

 

In the BGP routing table of Router 2 both prefixes for LoopBack ip addresses of Router 1 are received and valid:

 BGP Local router ID is 192.168.223.3

 Status codes: * - valid, > - best, d - damped, x - best external, a - add path,

               h - history,  i - internal, s - suppressed, S - Stale

               Origin : i - IGP, e - EGP, ? - incomplete

 RPKI validation codes: V - valid, I - invalid, N - not-found

 Total Number of Routes: 2

        Network            NextHop        MED        LocPrf    PrefVal Path/Ogn


 *>i    10.1.1.1/32        192.168.223.2   0          100        0       i

 *>i    192.168.223.100/32 192.168.223.2   0          100        0       i


But only one prefix is being installed in the ip routing table:

display ip routing-table

Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route

------------------------------------------------------------------------------

Routing Table : _public_

         Destinations : 8        Routes : 8


Destination/Mask    Proto   Pre  Cost        Flags NextHop         Interface


       10.1.1.1/32  IBGP    255  0             RD  192.168.223.2   Eth-Trunk10.621

       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

  192.168.223.0/24  Direct  0    0             D   192.168.223.3   Eth-Trunk10.621

  192.168.223.3/32  Direct  0    0             D   127.0.0.1       Eth-Trunk10.621

192.168.223.255/32  Direct  0    0             D   127.0.0.1       Eth-Trunk10.621

255.255.255.255/32  Direct  0    0             D   127.0.0.1       InLoopBack0


The customer asks why the second prefix (192.168.223.100/32) is not installed in the ip routing table.


Alarm Information

No alarm.

Handling Process

1) Have checked the configuration is ok.

2) Search the product manual for relative issue and found BGP supernet route will not be installed in ip routing table.

Root Cause

192.168.223.100/32 is with next hop 192.168.223.2/24, so it is a BGP supernet route for R2. NE20E router will not install supernet into IP routing table. Any route that meets one of the following conditions is a BGP supernet route.

·       If you perform bitwise AND operations on the destination address mask with the destination address and next hop address, respectively, the calculated network addresses are the same, and the destination address mask is greater than or equal to the next hop address mask.

·       If you perform bitwise AND operations on the destination address mask with the destination address and next hop address, respectively, the calculated network addresses are different. However, if you perform bitwise AND operations on the next hop address mask with the destination address and next hop address, respectively, the calculated network addresses are the same.

Solution

Ask the customer to user other BGP none-supernet route for test.

END