Broadcast-forwarding

[chieftan999]

Hi All,

Probably an easy question to anser:-

How do you configure either Broadcast-forwarding or directed-broadcast on a router interface?

 

[ccif1024]

You're probably looking for ip helper-address. It goes on the local inside (probably ethernet) and redirects many (not all) broadcasts into unicasts to a certain destination IP address on the other side of your network.

int faste0/0
ip address 10.10.10.1
ip helper-address 1.1.2.1

I don't have the exact broadcasts supported (or Forwarded) but Cisco's web-site does.

 

[lui3]

ip helper address will forward the following by default

bootp server
bootp client
tftp
netbios over ip 135

and four others i can't remember

to allow broadcast forwarding on a interface you can either bridge the interface or use the following command

ip directed-broadcast

this will forward all ip based broadcasts

ie 192.168.1.255(all packets addressed to the address in a broadcast packet will be forwarded. Used in SMURF DDOS attacks) for a network 192.168.1.0

 

[chieftan999]

Thanks all.

I have used the ip directed-broadcast command and also the helper-address command, but the receiving networks is still not getting the broadcast.

If I send to a single machine it gets the information okay, but the broadcast will not work.

For example:-

I am using a 10.67.0.0 255.255.255.0 network so the broadcast address will be 10.67.0.255. If I send information to the broadcast address it does not get there, but if I send information to 10.67.0.11 for example it does get there.

 

[lui3]

try ip helper-address x.x.x.255

with the ip helper address being the broadcast address of the network you are trying to communicate with

 

[MTandSAV]

Just to add to lui3 post, these are the 8 that are forwarded by default.


TACACS service
Domain Name System
Time service
IEN-116 Name Server
Trivial File Transfer (TFTP)
NetBios Name Server
NetBios Datagram Server
Boot Protocol (BootP) client and server datagrams

This link might be usefull for helper/broadcast addressing

http://www.cisco.com/univercd/cc/td/doc/product/software/ssr83/rpc_r/48383.htm

 

[chieftan999]

Thanks all for you help with this problem.

I have managed to solve the problem using the following:-

IP forward-protocol UDP 5007

Under the specified interface:-

ip broadcast-address 10.67.0.255
ip helper-address 10.67.0.30
ip helper-address 10.67.0.31
ip helper-address 10.67.0.32
ip helper-address 10.67.0.33

and it all works fine now.

Thanks again.

 

[gconnect]

What type of traffic are you trying to forward. I have used the 'ip forward-protocol udp' command to forward traffic. If you use the 'ip helper-address' command in conjunction with this, you can forward this type of traffic to the addy specified in the helper-address command


-gC-


XXXXXX-rtr(config)#ip forward-protocol udp ?
<0-65535> Port number
biff Biff (mail notification, comsat, 512)
bootpc Bootstrap Protocol (BOOTP) client (68)
bootps Bootstrap Protocol (BOOTP) server (67)
discard Discard (9)
dnsix DNSIX security protocol auditing (195)
domain Domain Name Service (DNS, 53)
echo Echo (7)
isakmp Internet Security Association and Key Management Protocol (500)
mobile-ip Mobile IP registration (434)
nameserver IEN116 name service (obsolete, 42)
netbios-dgm NetBios datagram service (138)
netbios-ns NetBios name service (137)
netbios-ss NetBios session service (139)
ntp Network Time Protocol (123)
pim-auto-rp PIM Auto-RP (496)
rip Routing Information Protocol (router, in.routed, 520)
snmp Simple Network Management Protocol (161)
snmptrap SNMP Traps (162)
sunrpc Sun Remote Procedure Call (111)
syslog System Logger (514)
tacacs TAC Access Control System (49)
talk Talk (517)
tftp Trivial File Transfer Protocol (69)
time Time (37)
who Who service (rwho, 513)
xdmcp X Display Manager Control Protocol (177)
<cr>