we here at cisco biscuits, are huge fans of simulation, why spend million pound on a room full of router death when for absolutely no money you can have a network that would make the average Service Provider quake in their booty, big respect to toxic for his stirling work in helping me get all this running back at the internest GNS3 is the logical culmination of the stirling work done by Christophe Fillot at the University of Technology, Compiegne, France, the dynamips Cisco® router emulation software. 
GNS3 packages the most useful routers, from the humble 2600’s to the fearsome 7200’s in a handy network designer, and allows them to run full ios images, and allows you to telnet, or ssh to each… so you are no longer using a simulator, you’re using a virtual machine, which you could, in theory, stick in the middle of an ISP network and save millions on hardware and electricity… i’ve been spanking the lab work for the bsci using gns3 and so far have configured multiple ospf areas, all flavours of bgp routing and route mapping, so far the only thing i can’t do with it is run IGMP with real switches, as GNS doesn’t (yet?) support switches, if you have a big bag of lab work to rinse out, this really is the answer, while Packet Tracer is good, it still has the limitations of any simulator, and it can be a proper pain in the arse to use..
general advice when running GNS3
- go out and buy the fastest machine you can afford with as much memory as humanly possible, as the hardware is all being emulated, mucho mips and flops are required, especially when you running 3 or 4 routers. i am running gns3 on an athlon xp 1800 with one GB of RAM, and one or two VM routers will sometimes lock up, or features refuse to work, i tend to kill all non mission critical processes while running
- choose the smallest IOS image you can get away with, when we first set up GNS we ran the advanced ip services image on 7200 routers [because we could] but the size of the image thrice multiplied was too much for my puny machine to cope with and much paging and CPU maxing was in evidence, toxic found a nice 2691image that so far has supported all of my BSCI needs [he later tells me that this image is a bit cranky]
- installation on windows gave us a little distress [toxic reports that it behaves very well in linux {no surprise there}] and the GNS3 implementation of the dynamips console still doesn’t work properly on my machine, and due to the tendency to crash i have been saving my topologies and configs at regular intervals, to enable saving of configs you must create a new project, after that all saves will automatically save configs, you will lose connection to all routers when you create the new project however, so ensure that a copy run start is performed so that when you re-open your project file you haven’t got to re-configure [truly a real killer on some multiple BGP beast at 2 in the am]
more..
so my man toxic hooked me up with a 64 bit athlon machine with a whole 2GB, RAM up session, after nuff fussing and fighting with ubuntu, didn’t like my ati viddy card, and gns3 is still kinda experimental for ubu, i gave in and went the xp64 route..
the first probelem was the path to dynamips, it being a 32 bit app, it gets installed in the Program Files (x86) directory, so you need to add the (x86) bit, so far so good.. now the hypervisors [that's what gns calls the virtual routers] are running but the console isn’t working, telnet is not happening, so i downloaded putty and stuck that in the path in gns3’s general settings and boom, the machine is cranking, three 7200’s running the daddy c7200-advipservicesk9-mz.124-4.T1,
so next up is to get gns talking to the ethernet loopback adapter on the xp box and via that hopefully we can get it talking tothe free TACACS+ server that’s floating about on the net, c’est la, see you when it’s done
September 2nd, 2008 | Tags: bsci, ccna, ccnp, ios, simulator | Category: routing, simulator | Comments (13)
