RE: ICMP [7:61004]
Yes,the host places this entry into its routing table. -Original Message- From: maine dude [mailto:[EMAIL PROTECTED]] Sent: Tuesday, January 14, 2003 2:56 PM To: [EMAIL PROTECTED] Subject: ICMP [7:61004] 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? Thanks in advance. -DJ - With Yahoo! Mail you can get a bigger mailbox -- choose a size that fits your needs **Disclaimer** Information contained in this E-MAIL being proprietary to Wipro Limited is 'privileged' and 'confidential' and intended for use only by the individual or entity to which it is addressed. You are notified that any use, copying or dissemination of the information contained in the E-MAIL in any manner whatsoever is strictly prohibited. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=61005t=61004 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: ICMP [7:61004]
=?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=7i=61048t=61004 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: ICMP [7:61004]
Hmm...that suggests that a VLSM-aware redirect would be useful. Send the mask along with the network address in other words. Does such a thing exist, or has it ever been proposed? 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=7i=61052t=61004 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: ICMP [7:61004]
I think Priscilla gives some good reason why a VLSM-aware redirect may not be very effective. Also redirects for default route or networks outside of your IGP would be problomatic. Dave Black Jack wrote: Hmm...that suggests that a VLSM-aware redirect would be useful. Send the mask along with the network address in other words. Does such a thing exist, or has it ever been proposed? 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 -- David Madland CCIE# 2016 Sr. Network Engineer Qwest Communications 612-664-3367 You don't make the poor richer by making the rich poorer. --Winston Churchill Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=61061t=61004 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: ICMP [7:61004]
Black Jack wrote: Hmm...that suggests that a VLSM-aware redirect would be useful. Send the mask along with the network address in other words. Does such a thing exist, or has it ever been proposed? I don't think such a thing has been proposed. Also, it may not be practical. The router sending the Redirect might not know about the subnet masking being used elsewhere on the network either? I guess it would depend on the routing protocol. There are always tradeoffs. It's probably a good thing that the host receiving the Redirect for Network places a host-specific route into its routing table, for all the reasons already mentioned (classless addressing, VLSM, discontiguous subnets.) But what's the tradeoff? ? give it some thought don't want to give it away right away think. analyze ideas? It might be obvious, but the tradeoff is that the host could end up with a bunch of host-specific routes in its table. It sends to 10.0.0.1, gets a redirect, places the host-speficic route in its table. It sends to 10.0.0.2, gets a redirect, places the host-specific route in its table. Etc. So, what's so bad about that? Well, it's extra processing and it uses a little extra memory (not a big deal these days, granted!) But as the list gets longer, lookups and placing new entries will take longer and longer. So some delay might occur. Just some more thoughts to get y'all thinking! :-) Priscilla 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=7i=61063t=61004 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
