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BT Business Hub 3.0 - Possible ARP issue?

elitt
Member

I am setting up an internal firewall (juniper SRX) on our new BT business hub. The setup seemed very straightforward, I have given the SRX a public facing IP address within our static range - this was done from the hub itself rather than my SRX. At first I thought I had no connectivity as I couldn't get internet access, however - if i ping the external ip for the gateway from the SRX, all of a sudden everything works OK. When I stop pinging, within afew seconds the connection drops again. This made me think that it is arp related and maybe the SRX isn't responding to ARP requests, but the Hub is? Also I can't ping the hub on 192.168.1.254 from the SRX - I think I should be able to. I know my SRX is fine - works perfectly on a different line.

 

Has anyone else seen this problem or is there something obvious I am missing?

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Accepted Solutions

elitt
Member

I resolved this, here is the solution in case anyone has the same problem. It was an arp issue. by default the juniper SRX doesn't respond to ARP requests on a different network. As the hub is on 192.168.1.x and my juniper is on the external range - it doesn't respond. 

Adding the setting : arp-resp unrestricted; on the untrust interface on my SRX fixed the problem.

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1 REPLY 1

elitt
Member

I resolved this, here is the solution in case anyone has the same problem. It was an arp issue. by default the juniper SRX doesn't respond to ARP requests on a different network. As the hub is on 192.168.1.x and my juniper is on the external range - it doesn't respond. 

Adding the setting : arp-resp unrestricted; on the untrust interface on my SRX fixed the problem.