I have two remote offices that I am currently replacing P2P links in and upon review of the routers in the main and remote offices, I noticed that there are tunnel interfaces configured to route via a Loopback interface. These older circuits are DS3 lines, and the new circuit is a fibre link that is basically metro ethernet between the sites. My question is, what is the purpose of the tunnel interfaces? I don't see any crypto lines to enforce encryption or anything like that, the only reason I can see for them would be for QoS reasons since our VoIP system does span the WAN links. Any input would be appreciated.
The first office I cut over I used a simple subinterface with Vlan tagging, since that is now the fibre circuit is supposed to work and the line came up fine. I'm just affraid I am over looking something. I am good with firewalls and switches, but I don't touch routers every day, so I am looking for a sanity check basically.
Would it be possible to post the configuration of the two routers? It would help us in understanding what the Tunnel interfaces could have been used for.
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As Peter notes, configs might help. Some reasons for running tunnels include conveying site-to-site routing info or site-to-site multicast.