Junos: L2Circuit over GRE with fragmentation configuration

A customer has asked me to work out how to get layer-2 traffic from a Juniper SRX, across the public internet and back into another SRX so that they can conserve IP address space. I worked the followign out in the lab, using a pair of SRX240s, and a pair of Cisco routers to simulate the public internet. Crucially, fragmentation of large packets is important, since MTU sizes across the internet could be variable. GRE tunnels don’t fragment by default, but this configuration permits that.

There might be scalability issues with the configuration as shown below, so it needs more work doing to it, but it at least proves that this is possible.

What we’re doing here is running MPLS over a GRE tunnel across the Internet, and putting a layer-2 circuit (Circuit Cross-Connect as Junos calls it) over that.

Trunking and sub-interfaces on the same switchport

For some reason, I never knew that you could trunk and use a sub-interface on the same port of a Catalyst 6500, so I’m recording it here for personal reference.

What I wanted to achieve was to connect two 7600 routers over an Ethernet pseudowire (E-Line, EoMPLS circuit, AToM circuit, Martini circuit – whatever it’s called these days).   The reason I needed to do so was that the interveninig 6500 routers were only getting a default route via BGP from the 7600s.

Juniper L2Circuit Config

Just posting a basic l2circuit configuration for my own reference… Piece of cake really, but it won’t work unless you use a dynamic routing protocol – the static that I had configured wasn’t enough.