BGP on Multihomed brings DNS Problems

RouterOS Forwarding Protocols
1

Hi All. I have been networking small environments and using RouterOS for many years, but this is my first foray into BGP.

A client has just setup a second circuit to the same ISP. The ISP’s network person configured our router’s BGP config, and a second person there has looked at it. From what I can tell from the Mtik Wiki, the BGP is configured correctly.

But we are seeing this odd DNS problem. The client’s customers cannot access a select few sites (apple.com, ebay.com, some others) when using the DNS servers from the client’s ISP. When we use other DNS servers there is no problem. The ISP has no other clients complaining of DNS issues. We are not seeing the Ping-Pong effect like “Premier” was seeing (in a different thread).

Can someone recommend where I should start looking to troubleshoot this? Thanks.

2

Can you reproduce the problem?

If so on an affected host:

  1. Ping/trace the DNS server, reachable?
  2. test the affected website using nslookup specifying different DNS servers
  3. Packet Capture the process see if you can find whats missing

Run similar tests on unaffected host to compare results (ping/trace not always reliable)