arp broadcasts on comcast

Hi Folks,

I'm watching my linux router going sort-of nutty and ran some tcpdumps.
What I found was a ton of arp who-has messages. Over a 15 minute period,
I got this many messages, from these hosts. I'm guessing that the .1
hosts are comcasts, but I have no idea. They resolve to this type of name:
host 12.246.199.1
1.199.246.12.in-addr.arpa domain name pointer 12-246-199-1.client.attbi.com.

Is this normal?

Thx, Chris

12.246.197.1 23
12.246.10.170 52
10.183.128.1 116
12.246.94.65 133
12.246.92.1 137
12.246.91.193 147
12.246.94.193 226
12.246.92.193 245
12.246.93.129 354
12.246.15.129 360
12.246.90.129 387
12.246.15.1 390
12.246.12.1 468
12.246.199.1 652
12.246.13.1 834
12.246.14.1 855
12.246.226.1 1128
12.246.236.1 1212
67.161.173.1 1286
12.246.10.1 1317
12.246.238.1 1390
12.246.8.1 1727
67.166.129.129 1874
67.164.231.129 2264
12.246.0.1 2290
67.161.172.1 2701
67.169.239.1 3892
12.246.4.1 4127
67.166.152.1 4836