my 2day journey into cisco routers Need icmp help

[CntrlAltDlt]

Ok 2 days ago the guy at my work who managed the pcs got fired well in the mean time he wiped the router config out and completely fdisked the drive to a laptop that run our heat and air by johnson controls metasys system to say he was a little pissed..about losing hes job but was a big mess though. Having worked on pcs for several years and never touching a router especially a cisco one at that. I spent a day and a half reading and configuring the network back ok finally got it back online but i am a bit confused on icmp.. 1.(why would you need icmp) 2.(how would you go configuring icmp.) 3. (what exactly does it do) the only thing i can figure is to let someone ping or traceroutes to let you know the status of the network and to inform you when it is down is this really needed when you have a onsite tech all the time.. heck its only 6 computers on this T1 line just sending email...

 

[wybnormal]

You are on the right path. ICMP or Internet Control Message Protocol is for PINGing and traceroute. It's also used on some custom apps that I have run across.

Why do we need it? Well.. this is how ping works. It's also how traceroute works but TR is a bit different. On the Tx it uses UDP and the return side it uses ICMP to carry the message(there are several) back to the host for decoding and then the host puts the results on your screen.

PING is one of the easist ways to make sure a host can see another device on the network. Traceroute provides a way to verify the connectivity like ping but it gives the path info.. or it gives the failure point unlike ping that says "host unavailable" or other such verbage

MikeS
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http://www.packetattack.com

"The trouble with giving up civil rights is that you never get them back"

 

[marsd]

Icmp is the combined messaging and error messaging layer
of IP. This protocol is vital unless you want to break
your ip stack entirely. You must do research on your networks traffic and icmp to decide whether blocking or
breaking icmp traffic for one function is allowable.
I had a network with linux and novell dns servers together
that would not function well without allowing ping tests as they were part of the implementation. YMMV.
This is a large topic and goes far beyond ping and traceroute. We are talking about network error messages
and fragmentation that may be fscked by not allowing icmp
types through.