Frequent Visitor
•
8 Messages
Comcast Modem broken in bridge mode after maintenance (dropping packets)
This is more informational for anyone who is experiencing a similar issue. Recently Comcast performed some sort of maintenance in my area (Splitting a node or something, not sure). After this maintenance was completed my internet connection started dropping packets left and right. I was looking at around 30% packet loss.
Comcast, as usual, is of no help. So I started troubleshooting on my own and noticed the connection was stable outside of bridge mode. So after looking into what could possibly cause this, it turns out after the maintenance the gateway is now expecting more frequent ARP requests. The default of 1200 seconds is no longer good enough for this new gateway Comcast setup and I had to drop it all the way down to 60 seconds for it to be stable. I don't know why Comcast changed their requirements and on top of it didn't notify anyone of it (it's Comcast so i guess i shouldn't be surprised). If anyone out there is running their own router with their Comcast modem in bridge mode and suddenly their connection starts dropping packets, BUT the connection is fine when bridge mode is disabled please look into reducing your ARP cache timer.
I'm running pfSense so I had to add the following line to the /etc/sysctl.conf file:
sysctl net.link.ether.inet.max_age=60
You may need to adjust your ARP cache timer with other models of routers if you run into this issue.
jeremyhu
Visitor
•
1 Message
2 years ago
Thanks so much for this. I have an XB3 that I just got and was having issues in bridge mode. I stayed connected for about 1-2 minutes and then droped for about 10 minutes before eventually reconnecting. I also discovered that I could get back to (temporary) working state by replugging the ethernet cable.
I gave up and went with double-NAT and DMZ to get things online, but that quickly fell apart (in part because because DMZ and port forwarding don't actually forward some pretty important ports like 80 and 993). So I'm really glad I noticed your post here.
I've got a Ubiquiti Security Gateway, and it has a default of 10 minutes. I moved it down to 60s and the issue seems to be resolved. Anyone else in the same boat can take a look at https://www.youtube.com/watch?v=SVKNGiDDeQk for a recent video about how to reduce the cache timeout.
(edited)
0
0
SweetBrown2012
Visitor
•
1 Message
1 year ago
Thank you for root causing this issue!
For anyone else who stumbles upon this using pfsense (including future me), you can make the adjustment in the GUI.
Click System > Advanced > System Tunables
Add a new entry:
Tunable Name = "net.link.ether.inet.max_age"
Value ="60" (I personally found 240 to be sufficient.)
Cheers!
0
0