Friday, January 8, 2021

Any BGP Ninjas out there? I really need some help troubleshooting an issue.

Hello guys. I would ask cisco but we are broke and I have no support on my gear. Imagine my pain.

I have two ISPs and two Transit routers (cisco 7604s)

Currently I'm getting a just a default route from ISP-A and a full table from ISP-B. Local pref is set higher for my ISP-B and Im using BGP communities on my ISP A to make route to my AS from ISP B more desirable. I've verified that Inbound traffic is coming from my ISP-B and outbound traffic is also going out via my ISP B. Of course I have iBGP between the two TRs.

Everything was great until this morning when I asked my ISP B to also send me JUST the default route. As soon as that happened, I started getting massive packet loss. From my ISP B Transit router, i could ping out just fine sourcing from any public interface (i have a bunch). From my ISP A Transit router If i pinged outbound i would get like 30 to 50% packet loss. On my ISP A Transit, i could see i had no route for say 8.8.8.8 and default route was coming from ISP B TR. I could ping between the Two Transit routers just fine. I shut off peering all together with my ISP A (neighbor shut) and i was still getting packet loss! I asked my ISP B to roll back and as soon as they sent me the full table, i was able to ping out without loss from my network! Can anyone shed any light here for me? I'm really confused as to why this would happen.

Thanks in advance.



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