Getting Multihomed - Part 3/3

Following up to one of my first posts. We FINALLY brought up BGP with all of our providers. A call from our CEO to some people at Verizon got some things moving again. I had the circuit up with BGP the same day. Pretty amazing, huh?

Anyways, now my problem was dealing with the limited memory and tcam allocation for unicast routes. If you recall, I ordered three full BGP feeds from three different providers. With the internet pushing 226,000 routes my 3750G wasn't going to cut it:

sh platform tcam utilization

CAM Utilization for ASIC# 0 Max Used
Masks/Values Masks/values

Unicast mac addresses: 400/3200 13/44
IPv4 IGMP groups + multicast routes: 144/1152 6/26
IPv4 unicast directly-connected routes: 400/3200 13/44
IPv4 unicast indirectly-connected routes: 1040/8320 1023/8134
IPv4 policy based routing aces: 512/512 2/2
IPv4 qos aces: 512/512 8/8
IPv4 security aces: 1024/1024 23/23

Note: Allocation of TCAM entries per feature uses
a complex algorithm. The above information is meant
to provide an abstract view of the current TCAM utilization

So now I've got full feeds from three providers coming in. Luckily I read up on IOS route-map statements before I brought these BGP sessions up. Otherwise things could've gotten ugly. Here's what I started with:

ip as-path access-list 50 permit ^174$
ip as-path access-list 50 permit ^4323$
ip as-path access-list 50 permit ^701$

I started with just getting the ASNs we were directly connected to. And my tcam started to fill, but it wasn't close. I thought, hey, why not get some more routes while I can? I started to read up a bit more on route-maps and I figured out how to get other ASNs into my route table. I only want the networks of providers connected to my providers. Does that make sense?

Without being able to see the full table I would have no idea of what I was doing. What if I wanted Level(3)'s routes, for instance? I needed to see what was going on. Luckily an old client of mine runs FixedOrbit - the coolest site to look at BPG information. All I had to do was query my directly connected ASNs and start picking other routes I wanted. BGP would take care of the rest.

Here is a shortened version of what I ended up with:

ip as-path access-list 50 permit ^174$
ip as-path access-list 50 permit ^174_3356$
ip as-path access-list 50 permit ^174_33363$
ip as-path access-list 50 permit ^4323$
ip as-path access-list 50 permit ^4323_1668$
ip as-path access-list 50 permit ^4323_6983$
ip as-path access-list 50 permit ^4323_11456$
ip as-path access-list 50 permit ^701$
ip as-path access-list 50 permit ^701_19262$
ip as-path access-list 50 permit ^701_3356$

Now I have entries in my route table for my directly connected ASNs (174, 701, 4323) and some ASNs they are peered with - 3356, 33363, 1668, 6983, 11456, 19262. I don't have much room in my tcam but hey, that's what VXRs are for! Wow, I really want one of those (with an NPE-G2, of course) ;).