04-11-2024
05:48 AM
- last edited on
04-11-2024
05:55 AM
by
rupeshah
Hi,
I having some issues with my GRE tunnel. The traffic between sites are going through the GRE tunnel, so clients traffic is not affected. I have two issues that I have found. The first one is the duplicate ping replies. Whatever I ping, there is a duplicate response. I checked the route and the only route is through the GRE tunnel. There is no duplicate IP. The routing is done via OSPF point-to-point. the MTU seems to be fine. However, when I removed the GRE tunnel, the duplicate response went away.
The second issue is I could not SSH in to the Cisco switch stack. The switch is a collapsed core and this is where the GRE tunnel getting terminated. I have an ACL on the switch's VTY. When I SSH-in from the other site (from the other end of GRE tunnel), the SSH would timeout. If I SSH-in locally within the site, it worked just fine.
I ran a packet capture on the client and I seen the 3-way handshake established, but there was a SYN ACK retransmission. After 3-way handshake, the first SSH packets went to the Cisco switch (The VTY ACL incremented) but the switch didn't respond. In Wireshark, it showed several TCP retransmission from the client to the server.
This has worked before. These issues started ~1 - 2 weeks ago. I know there is a firewall between my two sites. The firewall is managed by someone else. I do not know at this point if the firewall is playing a role with the issue we are experiencing.
I am looking for ideas how to troubleshoot the duplicate ping response and the SSH issue.
Thank you
04-12-2024 10:05 AM
It’s difficult to understand how you can remove the tunnel and still have connectivity if there is a firewall in the middle.
Just a start anyway…HTH
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