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722K broadband connect problem - arp issue

2416 Views 4 Replies 2 Participants Last post by  bnborg
My 622 recently died and was replaced with a 722k (about which I am not happy). I just noticed the 722 isn't getting a broadband connection now, never had a problem with the 622. The 722 gets the proper DHCP config set, but fails the broadband connect test. So, after much messing around (different routers, etc), I put a packet-sniffer on the network to see what was going on. The 722 sends a broadcast arp request to find my gateway, and never gets a response. Normally, I'd say this was a problem with the gateway, but no other device on my network has a problem, and neither did my 622. I'm out of ideas. Below is a packet trace. You can see that xx.12 does a broadcast and gets a response. xx.16 (the 722) does a broadcast and gets nothing. BOTH of these are on the same router (and I've tried 3 different routers, btw). 12 always works, 16 never works. I've included the expanded packet for 16's request, looks fine. Anyone have any ideas? (and no, I don't use ATT, and yes, I've put it behind other routers)

Time Source Destination Protocol Length Info
2 0.039335000 Azurewav_02:dd:88 Broadcast ARP 42 Who has Tell
3 0.041220000 Netgear_46:5c:25 Azurewav_02:dd:88 ARP 60 is at 00:24:b2:46:5c:25
6 3.610808000 Echostar_ce:2b:32 Broadcast ARP 60 Who has Tell

Frame 6: 60 bytes on wire (480 bits), 60 bytes captured (480 bits)
Ethernet II, Src: Echostar_ce:2b:32 (00:08:89:ce:2b:32), Dst: Broadcast (ff:ff:ff:ff:ff:ff)
Address Resolution Protocol (request)
Hardware type: Ethernet (1)
Protocol type: IP (0x0800)
Hardware size: 6
Protocol size: 4
Opcode: request (1)
[Is gratuitous: False]
Sender MAC address: Echostar_ce:2b:32 (00:08:89:ce:2b:32)
Sender IP address: (
Target MAC address: Broadcast (ff:ff:ff:ff:ff:ff)
Target IP address: (
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Amazing how seeing something in a different format suddenly shows something you haven't noticed - note the request packet size. The one that works is 42 bytes, the 722 sends a 60 byte packet. Looking at arp requests on my network for a while, every other device sends a 42 byte packet, and they all work. Looks like the 722 sticks a trailer on the packet, and no one will answer it. OTOH, from what I can find out about arp packet sizes, 60 is a possible size. So, I'm still not any closer to a solution.
My conclusion - for whatever reason, arp is broken on the 722, which, combined with all its other problems, makes it a candidate for the 'most useless dvr' award. I want my 622 back.
After leaving the packet sniffer running for a while, I did see some other arp requests from other devices with a 60 byte payload. Interestingly, those got a response. So, the packet size itself isn't the determining factor.
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