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Re: The use of .0/.255 addresses.
On Sat, 26 Jun 2004, Tony Li wrote: > The .255 address is very likely to be a broadcast address from a > netblock of /24 or longer. I would suspect that folks are wary of > accepting packets from a broadcast address as that could easily be a > smurf. The .0 address was used as a broadcast address long ago and then > was deprecated, so the same rationale probably applies. I have a case where this is currently biting me. I've got a few small blocks of address space that I've chopped up into /32's for router loopback IPs. These are in /24's which have been subnetted with various sized customer subnets and then a /27 or so worth of router loopback /32's. One in particular is: interface Loopback0 ip address 220.127.116.11 255.255.255.255 I found some time ago that my home DSL connected network could not reach (telnet, ping, etc.) that router's loopback. Our monitoring system could, and several iBGP peers could, so I didn't notice the issue until one night when trying to do some work from home. What I've found is that one of our routers (7206 doing T1/DSL aggregation running 12.1T) has .255 issues. Yes, it does have ip subnet-zero & ip classless in the config. What's really odd is, from that 7206, I can traceroute to 18.104.22.168, but if I ping 22.214.171.124 from it, I get replies from another 209.208.6.x address on a connected T1 customer's CPE, as if the ping was sent out as a broadcast ping. #sh ip ro 126.96.36.199 Routing entry for 188.8.131.52/32 Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric 4 Last update from 184.108.40.206 on FastEthernet0/0.1, 00:46:47 ago Routing Descriptor Blocks: * 220.127.116.11, from 18.104.22.168, 00:46:47 ago, via FastEthernet0/0.1 Route metric is 20, traffic share count is 1 #ping 22.214.171.124 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 126.96.36.199, timeout is 2 seconds: Reply to request 0 from XXXXXXXXXX (209.208.6.xyz), 68 ms Reply to request 1 from XXXXXXXXXX (209.208.6.xyz), 68 ms Reply to request 2 from XXXXXXXXXX (209.208.6.xyz), 68 ms Reply to request 3 from XXXXXXXXXX (209.208.6.xyz), 68 ms Reply to request 4 from XXXXXXXXXX (209.208.6.xyz), 68 ms I suppose I'll give up on using the .255 IP, but I've not been looking forward to changing that as it means redoing half a dozen BGP peerings. ---------------------------------------------------------------------- Jon Lewis | I route Senior Network Engineer | therefore you are Atlantic Net | _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________