If you store the reverse mapping for the routers’ loopback interfaces in DNS or configure the name-to-address mappings with the ip host commands, you can use the ip ospf name-lookup global configuration command to display the OSPF router IDs as router names.

Ken McCoy sent me a short question:

At one point someone posted an article about a command you could run on the Catalyst switch that would give you back the distance of the cable between the switch and end device, but now I can't find it.

I remembered reading the same article and after I've figured out the underlying technology is called TDR (Time Domain Reflectometer), uncle Google immediately provided a reader tip from Csaba Farkas.

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My favorite provocateur has dreamed up another sensational story ... and even has numbers to back it up. Reverse engineering the increase in reported number of CCIEs and taking in account the estimated number of seats in Cisco's labs worldwide, he concluded that the pass rate for CCIE R/S is currently at 35% whereas in the past the rumors claimed it was only around 10%. The conclusions in the story should not surprise you ... it must be the braindumps and the devaluing of the CCIE program. Of course it's the braindumps: people like Petr Lapukhov, Jeremy Stretch, Arden Packeer, Joe Harris and tens of others (including yours truly) are dumping the contents of their gray cell matter into blogs and wikis, creating astounding amount of information that we've never got from Cisco in the past.

The CCIE preparation programs also cover an enormous amount of scenarios and variations, giving you lots of material to practice (BTW, when I was teaching CCIE preparation bootcamps 15 years ago, the pass rate of my students was over 90% as I simply forced them to configure all the possible stupidities Cisco IOS could do at that time). The tests don't have to get any easier; the participants (if the calculations are correct) are simply better prepared. Whether the increased number of CCIEs results in the perceived devaluing of the program is another question (remember: the supply/demand rules), but I am absolutely sure that people passing CCIE lab exam these days know approximately as much as those passing it two or three years ago.

Of course you could argue whether someone who did tens (or sometimes hundreds) of scenarios in his lab and then passed the CCIE test is an expert or a braindump cheater (let's wait for the first blog post that claims that), but I doubt anyone is able to remember so many recipes and apply the correct one without a profound understanding of the underlying issues.

It’s possible to design OSPF area boundaries to have primary- and backup Area Border Routers. I described the details in a long-gone article, and fortunately found its shadow (without the diagrams) on archive.org.

Would you like me to migrate that article to ipSpace.net? Send me a message and I just might do it...

I tend to forget whether I'm in configuration mode or not and often type the do command in exec mode or the show command in configuration modes. With the alias functionality you can make the show command a native command in the configuration modes; just configure alias configure show do show.

The “only” drawback of this approach is that IOS has zillion different configuration modes and you have to define the alias in each one of them (you could do it just in the most common ones … or try to remember to type the do keyword first :).

It looks like some people forgot that July and August are supposed to be summer months when everyone is off to the nearest beach enjoying the sun (or maybe the global warning has caused unusually rainy weather in some parts of the globe). Leading the pack is Petr Lapukhov (a few more weeks like this and I'll start suspecting he's actually an pseudonym for a group of people like Tony Li was rumored to be a decade ago), who described Per-VLAN spanning tree (PVST) protocol, Multiple Spanning Trees Protocol (MSTP) and Dynamic Multipoint VPNs (DMVPN) (this one is so long I'll probably never find the willpower to read it)

DMVPN is also covered by Jeremy Stretch (I'm starting to wonder what's the root cause for the sudden fascination with this solution), who also provided a nice introduction to EUI-64 IPv6 addresses, a very practical view on shaping-versus-policing dilemma and simple step-by-step introduction to 802.1X.

As one would expect, Joe Harris and Arden Packeer are also ignoring the summer temptations. Joe provided an interesting link to the CCDE practical exam demo and Arden is continuing with his "OSPF over Frame Relay" saga (a few more installments and he'll be getting close to Jordan's Wheel of Time).

And last but not least: Tim Riegert sent me a link to a page full of TCP/IP and IMS Sequence Diagrams. The diagrams serve as a demonstration of EventStudio System Designer capabilities, but they are still good.

BGP route reflectors have been supported in Cisco IOS well before I started to develop the first BGP course for Cisco in mid 1990s. It’s a very simple feature, so I was pleasantly surprised when I started digging into it and discovered a few rarely known details.

The Basics

Route reflector is an IBGP feature that allows you to build scalable IBGP networks. The original BGP protocol (RFC 1771) contained no intra-AS loop prevention mechanism; routers were therefore prohibited from sending routes received from an IBGP peer to another IBGP peer, requiring a full-mesh of IBGP sessions between all BGP routers within an AS.

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Summer is a great time to complete small tasks you've always wanted to do but never found the time to do them. Thanks to Jackbook, individual post pages on my blog now include the Related posts by category feature.

It’s obvious why two routers in the same OSPF domain cannot have the same router ID. However, requiring unique router IDs on OSPF processes running in different VRFs is probably too harsh, even though it does prevent confusion if two VRFs ever get connected through a customer site. Anyhow, if you have overlapping IP addresses on loopback interfaces in different VRFs, OSPF process might not start.

• Petr Lapukhov continues to write interesting stuff: recently he's covered WRR queuing parameters on Catalyst 3550, wrote an introduction to SNMPv3 and provided sample private VLAN configurations.
• Joe Harris discovered an interesting feature in IOS release 12.4(20)T: you can increase the Fast Ethernet interface MTU way beyond the 1500 bytes, making it easier to implement various MPLS solutions in switched LAN environments.

Browsing through the starred articles in my FeedReader, I also found two older articles:

• Brian McGahan describes the IP Multicast helper-map feature.
• Arden Packeer writes about 6to4 tunnels.

If you have to troubleshoot routers with long configurations, you're probably as fed up with the slow response of the show running-config command as I am. Unfortunately, there's not much you can do; the running configuration is reverse-engineered from various memory variables every time you ask for it and that process simply takes time if you've configured many parameters.

IOS release 12.2(33)SRB has introduced a fantastic feature: router configuration partitioning. The early seeds of this idea are already present in mainstream IOS releases. For example, you can display the configuration of a single interface, all class-maps or all policy-maps. The configuration partitioning gives you the ability to display access-lists, route-maps, static routes, router configurations ...

EIGRP was always described as the only routing protocol that can do unequal-cost load sharing. As it turns out, BGP is another one (although it's way more limited than EIGRP). For example, if you have two links into a neighbor AS, you can load-share across them proportionally to their bandwidth.

EBGP load balancing was introduced with the BGP 4 Multipath Support feature in IOS release 11.2. Initially, EBGP supported up to six maximum paths; IOS release 12.0(S) increased that value to 8, IOS release 12.3T to 16 and 12.2S (including 12.2SRC) to 16.