=?iso-8859-1?q?maine=20dude?= wrote: > > Hi All, > > Quick question- > > When a router sends a redirect to a particular host, how does > the host > > remember to use this in the future, does the ICMP place an > entry into the > > hosts routing table?
Yes, the host places the new routing info in its routing table. On a Windows machine, you can see this with the "route print" command. There are some caveats, however. One caveat is that the entry stays in the table for a limited time. Windows seems to only keep it in the table for 10 minutes. Another caveat is that Windows doesn't enter a route for the entire network, even if the ICMP Redirect that comes back is Redirct for the Network (Type 5, Code 0). Instead, Windows (and probably other operating systems) place a host specific route in the routing table. For example: 1) PC sends to 10.0.0.1 using router ABC 2) Router ABC sends back an ICMP redirect saying use router XYZ for that network. (Redirect for Net, Type 5, Code 0) 3) PC places in its routing table 10.0.0.1 255.255.255.255 XYZ So, why didn't it place the following entry in its table, considering that it received a Redirect for the network and not a Redirect for the host? 10.0.0.0 255.0.0.0 XYZ Give it some thought..... more thought..... do you have an idea..... trying not to give it away before you give it some thought.... Answer: The host can't know about subnet masks being used elsewhere. Also, with classless addressing, it can't assume a Class A mask for network 10.0.0.0. The host can't know for sure that ALL of 10.0.0.0/8 is reachable by the router that claims that it is. With variable-length subnet masking, classless addressing, discontiguous subnets and all the other things people do to their network designs, the safest thing for the host to do is to place a host-specific route into its table. Just thought I'd turn this into a more advanced "lesson." :-) _______________________________ Priscilla Oppenheimer www.troubleshootingnetworks.com www.priscilla.com > > > > Thanks in advance. > > -DJ > > > > > --------------------------------- > With Yahoo! Mail you can get a bigger mailbox -- choose a size > that fits your needs > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=61048&t=61004 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
