Dynamips Gotchyas
Dynamips is a great tool. Not everyone can afford to spend $15k or whatever on a rack with real routers but with Dynamips you can get most of the functionality out of a $750 PC.
I went down to MSY recently and got a PC to do the job. You need lots of RAM (4GB for my box), a beefy CPU (2.66GHz Core2Duo) and you’re on your way. Windows is a pain for Dynamips for a variety of reasons. I am using Ubuntu 7.10 as my OS. I am a Mac user normally but I couldnt be bothered trying to get OSX running on a yum-cha beige box when I can get Linux running in about 10 minutes…
GNS3 is the GUI version of Dynamips. I have made a Narbik topology in GNS3 and it does the job very well. Pitfalls are:
No Switch emulation. I run a 3640 with an NM-16ESW as a switch. It does probably half the job a real 35[56]0 does. No MST, no auto vlan creation from the interface (must use vlan database first), no vlan creation from conf t (once again use vlan database) and also cant auto detect duplex settings. I got around this by hard coding the duplex on the connected router ports.
Frame-relay wont auto-detect lmi-type. Simple… frame-relay lmi-type ansi.
3640s arent used in the real lab. No big deal. The IOS is the same (almost)… the only difference is interface numbering. What you need to watch out for though is the NM-16ESWs are only Ethernet and you cant get FE or GE blades for the 3640s. This affects spanning-tree costs and the like but its no big deal. If you are really pedantic you could manually asssign spanning-tree port costs and the like to interfaces… But I didnt bother unless my scenario asked me to.
