On Wed, Dec 23, 2015 at 03:17:10PM +0300, danilov wrote:
Hello.
I have a small network with several bird routers as bgp and ospf routers.
EBGP-session has been established between one of our bgp-routers and customer router with multihop feature through OSPF-domain and iBGP-domain.
Then bgp-router advertises the customer announce to other bgp-router, that also works as OSPF ASBR (ospf-domain on the one side and ibgp-domain on the other side). On this ASBR-router I see the valid next-hop value (customer router IP-address in OSPF-domain) in the corresponded routes of customer.
This routes are installed to OSPF-domain, but in the outgoing LSA-updates I see only 0.0.0.0 forward-address values instead the customer router IP-address (I have checked it with wireshark).
Brief flowchart:
(CUSTOMER-ROUTER)--(PE)--<ospf-domain>--(ASBR)--<ibgp-domain>--(BGP-ROUTER) \ / \-------------------EBGP session---------------------/
Hi If i undestand it correctly, the route flow is: CUSTOMER-ROUTER -> BGP-ROUTER via EBGP BGP-ROUTER -> ASBR via IBGP ASBR -> PE via OSPP ?
Some info from ASBR:
From bird command line.
bird> show route all XX.XX.102.0/23 export ospf_tst XX.XX.102.0/23 via YY.YY.0.210 on eth1 [bgp_tst_r1 12:41:09] * (100) [AS____i]
bgp_tst_r1 is an IBGP? What is its configuration? How that route looks on BGP-ROUTER? I am not really sure why there is 'via YY.YY.0.210', if it is from IBGP then there should be the next hop from recursive lookup of bgp_next_hop (WW.WW.6.32 from ZZ.ZZ.21.92/30). The current code in BIRD for exporting routes to OSPF will set up the OSPF forwarding address based on gw (YY.YY.0.210), not based on bgp_next_path (ZZ.ZZ.21.94). And only allow immediate next hop addresses (i.e., ones that are directly reachable without intermediate next hops). If your bgp_next_hop is an immediate next hop but for some reason different from 'via' address, you could fix that in OSPF export filters on ASBR by 'gw = bgp_next_hop', but that would not work if bgp_next_hop is not an immediate next hop. Generally, I am not sure if BIRD does the right thing in setting forwarding addressess for OSPF external routes. I cannot find a justification for restriction to immediately-reachable next hops, so perhaps that is an unnecessary restriction in BIRD and ASBR could just put bgp_next_hop here. Question is what is a reasonable default here. One possibility would be to ignore immediate next hops ('via'), have an explicit route attribute settable in export filter (e.g. 'ospf_fwd_addr') and originate external routes with zero forwarding addresses unless explicitly configured in filters. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."