How to summarize LTE mobile routes into BGP

[steve22076]

            Our basic architecture is that of two 1900 series routers, one running the primary Verizon MPLS T1 and the other connected with a backup LTE connection into the same MPLS cloud as our primary T1.   We have recently implemented a NAC implementation that required multiple /26 subnets.  To have these /26 subnets function over LTE in the case of failover they are advertised into the LTE mobile network by adding the sub-interfaces into the ip mobile-router configuration.   By doing this they are then advertised into the same MPLS cloud and BGP AS as the other primary connection.   On the primary router all these /26 subnets are required to be advertised into BGP as a single /24 in order to stay under our maximum prefix limit with the carrier.    The result of this is that our /26 NAC Vlans always try to take the backup LTE connection rather than the primary T1 connection because the mobile /26 route takes precendence over the /24 route we advertise in our BGP configuration on our primary router.  

     Is there a way to either summarize routes into a mobile network or force a /24 advertisement to take precedence over the /26 route created by the ip mobile-network entries?

Router 2 mobile configuration that puts /26 interfaces into BGP:

ip mobile router

address x.x.x.x 255.255.255.0

collocated single-tunnel

home-agent x.x.x.x

mobile-network GigabitEthernet0/0.9

mobile-network GigabitEthernet0/0.52

mobile-network GigabitEthernet0/0.53

mobile-network GigabitEthernet0/0.54

mobile-network GigabitEthernet0/0.55

mobile-network GigabitEthernet0/0.2

mobile-network GigabitEthernet0/0.56

mobile-network GigabitEthernet0/0.4

mobile-network GigabitEthernet0/0.57

Router 1 BGP configuration summarizing the 10.4.244.0 network as /24 due to prefix limitations:

router bgp 65413
bgp log-neighbor-changes
network 10.4.244.0 mask 255.255.255.0
network x.x.x.x mask 255.255.255.0
network x.x.x.x mask 255.255.255.255
network x.x.x.x mask 255.255.255.255
network x.x.x.x mask 255.255.255.0
network x.x.x.xmask 255.255.255.0
network x.x.x.x mask 255.255.255.0
network x.x.x.x mask 255.255.255.0
neighbor x.x.x.x remote-as 65000
neighbor x.x.x.x soft-reconfiguration inbound

Router 1's subinterfaces broken down into their /26's:

GigabitEthernet0/0.52      10.4.244.2

GigabitEthernet0/0.53      10.4.244.66

GigabitEthernet0/0.54      10.4.244.130

GigabitEthernet0/0.55      10.4.244.194

sh ip route result for the /24 of this network showing the router is receiving the /26:

RTR01#sh ip route 10.4.244.0

Routing entry for 10.4.244.0/26

  Known via "connected", distance 0, metric 0 (connected, via interface)

  Routing Descriptor Blocks:

  * directly connected, via GigabitEthernet0/0.52

      Route metric is 0, traffic share count is 1

Data center edge router "sh ip route"  When /26 mobile networks are configured under ip mobile router section of router 2 (backup LTE connected router)

vzb-rtr01#sh ip route 10.8.142.0
Routing entry for 10.8.142.0/26
  Known via "bgp 64900", distance 20, metric 0
  Tag 65000, type external
  Redistributing via eigrp 10
  Advertised by eigrp 10 metric 1000 1000 255 150 1400
  Last update from x.x.84.209 00:00:04 ago
  Routing Descriptor Blocks:
  * x.x.84.209, from x.x.84.209, 00:00:04 ago
      Route metric is 0, traffic share count is 1
      AS Hops 4
      Route tag 65000
      MPLS label: none

Data center edge router "sh ip route" when mobile networks are not configured under the "ip mobile router" section in backup router.

gsc-vzb-rtr01#sh ip route 10.8.142.0
Routing entry for 10.8.142.0/24
  Known via "bgp 64900", distance 20, metric 0
  Tag 65000, type external
  Redistributing via eigrp 10
  Advertised by eigrp 10 metric 1000 1000 255 150 1400
  Last update from 68.137.84.209 3w6d ago
  Routing Descriptor Blocks:
  * x.x.x.209, from x.x.x.209, 3w6d ago
      Route metric is 0, traffic share count is 1
      AS Hops 2
      Route tag 65000
      MPLS label: none

[paul driver]

Hello

Can you post a simple topology so to visualise this setup a bit better

Res
Paul

Sent from Cisco Technical Support iPad App

[Jon Marshall]

Steve

I initially thought the problem was that you were advertising a /24 into BGP on your primary link and then /26s via the backup link so that remote sites running would prefer the backup link. But then from your post -

RTR01#sh ip route 10.4.244.0

Routing entry for 10.4.244.0/26

  Known via "connected", distance 0, metric 0 (connected, via interface)

  Routing Descriptor Blocks:

  * directly connected, via GigabitEthernet0/0.52

      Route metric is 0, traffic share count is 1

this is showing as connected and is therefore taken from one of the 2921s, presumably the primary router. So are you aksing a different question to the one i was assuming ie. i would have expected you to post a "sh ip ro ..." from a remote site BGP router.

In answer to your specific query i don't know about summarising mobile IP networks but i don't think you can force the /24 to be preferred over the /26s in BGP because the most specific prefix is always chosen first before any of the attributes are considered.

If the problem is with the remote sites preferring the backup link do you advertise all your subnets (excluding the mobile IP subnets) down both the primary and backup links or just a subset of the subnets down the backup link ?

Jon