Is Internet Melting Down?
A while ago I’ve read a post about the potential Internet meltdown by Michael Morris. He provided an amazingly accurate analysis of the facts … and ended with a wrong conclusion. To understand the whole issue, please thoroughly read his text in its entirety before proceeding.
Back? OK. As I said, his analysis was great, but the conclusions were wrong. Regardless of whether we use IPv4 (and advertise smaller and smaller prefixes) or IPv6, the problem is the same: everyone wants to have chunks of non-aggregatable provider-independent public address space (so you can freely move between Service Providers) and everyone advertises these PI prefixes to multiple service providers (because multihoming is so cheap these days). Even networks that are not multihomed today use their own PI address space and private AS numbers to connect to a single ISP, so they could get multi-homed in a second if they feel like it.
… updated on Monday, December 28, 2020 10:32 UTC
Using EIGRP in MPLS VPN Networks
We described EIGRP-in-VRF in MPLS and VPN Architectures, Volume II. A few details have changed in the meantime; you have to configure the following features to get EIGRP running within MPLS/VPN environment:
- The autonomous-system command within the VRF address family is mandatory, even if the VRF AS number matches the EIGRP process number.
- The default BGP-to-EIGRP redistribution metric has to be configured, otherwise remote EIGRP routes will not be redistributed even though they have EIGRP metric encoded in extended BGP communities.
- Things work best if you disable auto-summary on PE-routers.
Static DHCP assignment for clients without client-id
A while ago I've installed Fedora Linux on one of my workstations and spent enormous amount of time trying to give it a static IP address from the Cisco IOS DHCP server. I though I was the only one dumb enough to have this problem, so I didn’t document my solution, but then one of the readers made a comment to the Assigning server IP addresses with DHCP post describing almost identical symptoms:
PPP default route
You do not need the route "ip route 0.0.0.0 0.0.0.0 Dialer0 10 track 100" and the tracking if you configure "ppp ipcp route default" on the dialer interface. Works the same way... :-)You might be wondering why Cisco's engineers decided to pollute IOS with yet another feature. The problem they had was the way PPP over Frame Relay is implemented: it uses virtual interfaces and although you have a very static connection, you cannot bind a static interface name to it. A dynamic interface (with potentially changing name) is cloned from the virtual template every time the PPP-over-Frame-relay session is started. Obviously you cannot configure a static default route pointing to it in advance, so you need yet another feature to do it (I'll not even try to figure out how to create non-default static routes pointing to cloned interface).
Display locally originated BGP routes
Displaying the BGP routes originated in the local AS is simple: you just filter the BGP table with a regular expression matching an empty AS path. Displaying routes originated by the local router is tougher. You could use the fact that the local routes have the weight set to 32768:
PE-A#show ip bgp quote-regexp "^$" | inc Network|32768
Network Next Hop Metric LocPrf Weight Path
*> 10.0.1.1/32 0.0.0.0 0 32768 i
This would work if you don’t play with BGP weights in network statements. If you’ve changed the weights, you should filter the routes based on the BGP next-hop: locally originated routes have the next-hop 0.0.0.0 and all other routes should have a non-zero BGP next-hop. To filter BGP routes based on the next-hop you have to:
Control Plane Protection logging does not work on transit subinterface
IOS auto-upgrade
Web 2.0 presentation
Display BGP routes originated in the local AS
The easiest way to display BGP routes originating in the local autonomous system is to use the regular expression ^$ (empty AS-path) in the show ip bgp regexp command, for example:
PE-A#show ip bgp regexp ^$
BGP table version is 10, local router ID is 10.0.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 10.0.1.1/32 0.0.0.0 0 32768 i
r>i10.0.1.2/32 10.0.1.2 0 100 0 i
If you want to apply a show filter to the printout of this command, you have to use the quote-regexp variant; otherwise the rest of the line is interpreted as regular expression. To skip the header explaining the BGP status code (we know them by heart by now, don’t we?), use …