From: Church, Chuck (cchurch@wamnetgov.com)
Date: Wed Jan 07 2004 - 11:26:09 GMT-3
William,
Your first sentence sounds like the definition of an ip helper address, but a helper address deals with an all-nets broadcast. I don't think it works with directed broadcasts. Ip helpers are limited to certain UDP protocols, and you can add/delete other UDP protocols. Enabling directed broadcasts on an interface enables the forwarding of all directed broadcasts, regardless of the IP protocol. Someone correct me if I'm wrong, but I believe that's correct.
Chuck Church
CCIE #8776, MCNE, MCSE
Wam!Net Government Services
13665 Dulles Technology Dr. Ste 250
Herndon, VA 20171
Office: 703-480-2569
Cell: 703-819-3495
cchurch@wamnetgov.com
PGP key: http://pgp.mit.edu:11371/pks/lookup?op=index&search=cchurch%40wamnetgov.com
> -----Original Message-----
> From: William Chen [mailto:kwchen@netvigator.com]
> Sent: Wednesday, January 07, 2004 3:48 AM
> To: ccielab@groupstudy.com
> Subject: Directed Broadcast Forwarding
>
>
> Dear all,
>
> In DocCD, it says: "You can enable forwarding of IP
> directed broadcasts on an interface where the broadcast
> becomes a physical broadcast. If such forwarding is enabled,
> only those protocols configured using the ip forward-protocol
> global configuration command are forwarded."
>
> However, in the following testing, I found that ICMP
> packets is also forwarded. Is there a wrong point in DocCD?
>
> R1#sh ip route
> Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
> D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
> N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
> E1 - OSPF external type 1, E2 - OSPF external type 2
> i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia
> - IS-IS inter area
> * - candidate default, U - per-user static route, o - ODR
> P - periodic downloaded static route
>
> Gateway of last resort is not set
>
> C 192.168.1.0/24 is directly connected, Serial0/0
> i L1 192.168.2.0/24 [115/20] via 192.168.1.2, Serial0/0
> R1#sh ip int brief | ex unass
> Interface IP-Address OK? Method Status
> Protocol
> Serial0/0 192.168.1.1 YES manual up
> up
> R1#p 192.168.2.255
>
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 192.168.2.255, timeout is 2 seconds:
> !!!!!
> Success rate is 100 percent (5/5), round-trip min/avg/max =
> 60/71/116 ms
> R1#
> *Mar 1 06:49:34.054: ICMP: echo reply rcvd, src 192.168.1.2,
> dst 192.168.1.1
> *Mar 1 06:49:34.082: ICMP: echo reply rcvd, src 192.168.2.5,
> dst 192.168.1.1
> *Mar 1 06:49:34.114: ICMP: echo reply rcvd, src 192.168.1.2,
> dst 192.168.1.1
> *Mar 1 06:49:34.142: ICMP: echo reply rcvd, src 192.168.2.5,
> dst 192.168.1.1
> *Mar 1 06:49:34.174: ICMP: echo reply rcvd, src 192.168.1.2,
> dst 192.168.1.1
> *Mar 1 06:49:34.202: ICMP: echo reply rcvd, src 192.168.2.5,
> dst 192.168.1.1
> *Mar 1 06:49:34.234: ICMP: echo reply rcvd, src 192.168.1.2,
> dst 192.168.1.1
> *Mar 1 06:49:34.262: ICMP: echo reply rcvd, src 192.168.2.5,
> dst 192.168.1.1
> *Mar 1 06:49:34.294: ICMP: echo reply rcvd, src 192.168.1.2,
> dst 192.168.1.1
> *Mar 1 06:49:34.322: ICMP: echo reply rcvd, src 192.168.2.5,
> dst 192.168.1.1
>
> Best Regards,
> William Chen
>
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