Migration Strategy: Moving From MPLS/LDP to Segment Routing

21 03 2019

MPLS core networks that use Label Distribution Protocol (LDP) are common in SP core networks and have served us well. So, the thought of pulling the guts out of the core is pretty daunting and invites the question why you would want to perform open-heart surgery on such critical infrastructure.   This article attempts to explain the benefits that would accrue from such a move and gives a high-level view of a migration strategy.

Why Do I Need Segment Routing?

  • Simplicity:   LDP was invented as a label distribution protocol for MPLS because nobody wanted to go back to the standards bodies to re-invent OSPF or IS-IS so that they could carry labels.  A pragmatic decision, but one that results in networks having to run two protocols.  Two protocols means twice the complexity.  
    Segment Routing simplifies things by allowing you to turn off LDP.  Instead it carries label (or Segment ID) information in extensions to the IGP.  This then leaves you with only IS-IS or OSPF to troubleshoot.  As Da Vinci reportedly said, ‘simplicity is the ultimate sophistication’. 

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MPLS-TP intro

14 03 2013

I thought this was a nice MPLS-TP intro from Ciena – not too much detail, and a bit oddly produced, but good all the same:





Junos: L2Circuit over GRE with fragmentation configuration

8 03 2011

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.

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Trunking and sub-interfaces on the same switchport

7 10 2008

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. Read the rest of this entry »





Juniper L2Circuit Config

3 01 2008

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.

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