NetworkTalk & BGP

B.3.b) Ibgp session within router RT-B.

1. For upload/egress traffic we need to receive the FIB of router RT-A in router RT-B and tag it with LocalPref 90.

As a result, for example, Zone-B customers will upload:

  • To ISP-C’s link (tagged with LocalPref 100).
  • If ISP-C link is cut, upload will go to ISP-B link
  • If ISP-C and ISP-B links are both down, to RT-A and so to ISP-D-Link1 (tag local pref100)
  • Etc.

 2. On RT-B, we tag with local-pref 90 the RIB received from the Ibgp speaker RT-A :

router bgp 1000
bgp log-neighbor-changes
neighbor ibgp_client peer-group
neighbor ibgp_client remote-as 1000
neighbor ibgp_client description “Peering with iBGP Core Routers”
neighbor ibgp_client password 7 “…”
neighbor ibgp_client update-source Loopback1
neighbor ibgp_client version 4
neighbor 11.11.226.26 peer-group ibgp_client
!
neighbor ibgp_client send-community both
neighbor ibgp_client next-hop-self
neighbor ibgp_client route-map IBGP-Neighbor-IN in
neighbor ibgp_client route-map IBGP-Neighbor-OUT out


route-map IBGP-Neighbor-IN permit 10
set local-preference 90

3. On RT-A, the FIB is sent to router RT-B :

router bgp 1000
bgp log-neighbor-changes
neighbor ibgp_client peer-group
neighbor ibgp_client remote-as 1000
neighbor ibgp_client description “Peering with iBGP Core Routers”
neighbor ibgp_client password 7 “…”
neighbor ibgp_client update-source Loopback1
neighbor ibgp_client version 4
neighbor 11.11.226.27 peer-group ibgp_client
neighbor ibgp_client send-community both
neighbor ibgp_client next-hop-self
neighbor ibgp_client route-map IBGP-Neighbor-IN in
neighbor ibgp_client route-map IBGP-Neighbor-OUT out


With the following route-map we advertise the FIB of RT-A to RT-B.

route-map IBGP-Neighbor-OUT permit 20


Note: blank or empty route-map will send all routes present in FIB.

Etc.

4. If we give a look to the Figure B.7, we can see that it not recommended configuring the soft-inbound option reconfiguration within our routers.

Since each ISP sends the full internet table (440k prefixes) the sums of network that the router has to put in copy asks a lot of CPU and memory utilization.

See below Figure B.7: Ibgp relations with BGP tables, RIB and FIB