BGP: Network statement or Redistribute connected?

Sonugnair_2 · ‎11-21-2008

Hi,

We have a central site consisting of 2 6500 switches and one 3800 router. There are about 30 remote locations connected via frmae relay and ISDN as backup with 1841 at branches. On the LAN side we use EIGRP as the routing protocol.We are in the process of migrating frame relay to Provider MPLS. The provider will place a PE divice at all locations. At the main site HQ our WAN router will have BGP peering with PE device.The WAN router in addition to having BGP peering with the provider will also have EIGRP peering with core switches. Then on the WAN router we do mutual redistribution between EIGRP and BGP. (This is how we plan to do it)

We have decided to have a test setup as follows:

R1--R2--PE1--Cloud--PE2--1841 router.

Router2 peers with PE1 using iBGP. 1841 router peers with PE2 using iBGP.

Assuming that the network between the 1841 and PE2 is 192.168.4.0/30 and the local LAN has networks 10.11.1.0,10.11.2.0 etc what is the best practise of "advertising" these networks. Is it to use the network statemanets or to use the redistribute connected statement under bgp configuration.

router bgp xxxxx

no synchronization

bgp log-neighbor-changes

network 192.168.100.4 mask 255.255.255.252

network 10.11.1.0 mask 255.255.255.0

network 10.11.2.0 mask 255.255.255.0

neighbor 192.168.100.5 remote-as xxxxx

no auto-summary

OR

router bgp xxxxx

no synchronization

bgp log-neighbor-changes

redistribute connected

neighbor 192.168.100.5 remote-as xxxxx

no auto-summary

Thanks in advance.

Sonu.

marikakis · ‎11-21-2008

Hello,

I prefer to avoid redistribution whenever I can (no redistribution, no redistribution bugs or less delays via interaction between different protocols).

In your scenario, with redistribution you seem to save some typing (1 redistribution command instead of 3 network commands) and you might need to add further networks in the future. However, redistribution would better be controlled via a route-map to avoid a network being redistributed unintentionally and unexpectedly. Whether you use a route-map for redistribution or use network commands, you would still need (for best practice reasons) to specify particular networks. So, less typing is probably not a factor to consider here.

Redistribution will cause the routes to be inserted into BGP with an origin of incomplete. This means that if two same routes exist, only difference being that one came via network command and the other via redistribution, the route originated via network command is preferred. This is not a serious issue, but it might confuse your general troubleshooting procedures (one more factor that determines BGP path selection must be considered).

Kind Regards,

M.

p.s. I forgot to say clearly that I would suggest the method that uses the network command (I thought I said that, but it seems to me that it is said in a quite indirect way).

d.cendan · ‎08-26-2016

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ปลาวาฬทราย RMUTT CPE IX · ‎08-18-2020

I think the redistribute static also, what's the best practise?

Giuseppe Larosa · ‎08-18-2020

Hello @ปลาวาฬทราย RMUTT CPE IX ,

I agree that for BGP it is better to use the network statement when possible to have better control.

Static routes are manually configured so they are known in advance. The next-hop or outgoing interface can fail but the network command in BGP reacts to the removal of the static route from the IP routing table by withdrawing the BGP prefix.

The use of redistribution should be reserved to other dynamic routing protocols like OSPF or EIGRP where you don't know in advance what subnets will be advertised.

However, there was a limitation to the maximum number of network statements that many years ago was in the order of 200.

Hope to help

Giuseppe