In this post we look at a way to filter labels in an MPLS environment. In many MPLS environments, labels are only needed for PE loopbacks and having LFIB entries for connected network is unnecessary. For this post we have the following topology with R1 and R3 as PE routers.

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In this post we will look at what happens to the TTL value of a packet when it enters the MPLS VPN. We will also see how we can change that behavior to hide the provider network from customers.

R4(CE)—R5(PE)—R9(P)—R8(P)—R6(PE)

R4 is a CE router communicating with a VRF on R6.

R6 is a PE but has a loopback in the VRF.

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In this post, we look at how MPLS and LDP are used to build an LSP between two BGP speaking routers. The routers will share IBGP routes with each other, however they will not share BGP routes with an intermediate router nor will they redistribute BGP routes into the IGP. Labels are used to forward packets the proper next-hop. For those familiar with MPLS VPN already, this works very similarly however we have no VRFs.

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Recently a good question was posted on Groupstudy asking why a router needs to know that an IPv6 address is an anycast address. I often wondered this myself and it turns out, the router does not perform Duplicate Address Detection as it does for normal unicast addresses. A small lab scenario will suffice to give use the results!

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As the name suggests, this feature allows routes with a specific tag to be installed in the RIB faster than other prefixes.  By default, the highest priority prefixes are ones with /32 masks. As we will see here, we can tag routes to give them a higher priority than /32 prefixes.

The command we will be using to see this in action is:

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