[c-nsp] Upgrading older 7600 with an ASR1000 router.. Questions..

Howard Leadmon howard at leadmon.net
Wed Dec 18 20:28:18 EST 2019

  I know a while back I had asked about replacing an old 7606/RSP720 I 
had handling routing, and I got some great info from the group that was 
much appreciated.    I ended picking up an ASR1000 series router to use 
in place of the 7606, or so I thought, I am wondering now if I actually 
still need both.

  The 7606 handled both Layer 2 and Layer 3 functions fairly well for 
us, for a great many years, and I guess I just got very used to this 
fact.  The one thing that always worked really well was that we had a 
bunch of Ethernet multi-point links from providers like Zayo and Comcast 
that interconnected a bunch of our different locations, as they were L2, 
I simply setup a tag that ran to a location and off it went.   Most of 
the remote locations are all 4500 series switches, so using L2 trunks 
made this just work.   So on the 7606, I had trunks to the various 
providers, as well as local trunks to some of the other switches in the 
racks,  my transit links, and a few clients.

  So enter the ASR1000 and I thought great, this is a simple change as I 
should just be able to copy most of my 7600 configs across into the ASR 
and life will be good.   The I went to setup a trunked port to bring the 
existing equipment into the new ASR.   Surprise, unlike the old 7600 
there is no turning a port in the ASR into a switchport, or not that I 
can find, so it looks very much like it's an L3 device for the most 
part.   Well that sure blows up all the vlan interfaces/trunks that were 
in the 7600 that will not transfer into the ASR.

  I am wondering if I need to keep the old 7606 in service to handle the 
L2 trunking terminations and pasthroughs, and just setup sub-interfaces 
on the ASR to handle any of the needed L3's connections that need to do 
routing via the ASR, like all of our transit and peering links?

  I actually have a couple L2 trunks, where some of the VLAN's are L3 
connections that I picked up on a VlanXX interface locally, but at the 
same time I also  have other L2 Vlan's that needed to come in one port, 
and then head back out another port to a different device.  I have 
googled around a bit, but heck if I see anyway to do this mixed 
environment on the ASR, where on my old 7600 it just worked, and has 
worked well for a great many years.   Heck the main reason I am ditching 
the old 7606 workhorse is that as we all know carrying full routing 
tables to multiple providers, well it's getting very long in the tooth 
without cutting out some routes.

  I am sure some here have had to deal with something like this at some 
point, so I hope someone can toss me some suggestions or insight on the 
best way to handle this, or do I just delegate the new ASR as just a BGP 
router, and still pass it all back through the old 7600 for now.

Thanks as always for any input on how to approach this task..

Howard Leadmon
PBW Communications, LLC

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