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A couple devices (usually) won't connect to the network
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chndrcks
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Joined: 27 Apr 2007
Posts: 4

PostPosted: Thu Dec 24, 2015 3:39 am    Post subject: A couple devices (usually) won't connect to the network Reply with quote

I have a Samsung blu ray player and a dlink webcam that almost never connect to the local network.

The setup is a Netgear R6250 in Access Point mode connected to a gentoo server which does NATing and DHCP for my home devices.

Here's everything I've tried:
Blu Ray player and Wifi router firmwares are up to date.

I tried a different router from a different brand.

Plugging the blu ray player into the wired network (through a port on the wireless router) works, which is odd because the wireless router is set to Access Point mode and the server doesn't differentiate wired and wireless traffic, so there should be no difference between the two.

That lead me to think that the wireless card was the problem, but I've ruled that out too.

I plugged my mbp into the wired network and turned on Internet Sharing over WiFi and connected the blu ray player to that. The player worked with that configuration.

When I have weird networking problems, I tend to think MTU issues, but I've set the lan and wan NICs on the server to different MTUs with no change (and often that just caused other devices to break).

I had given up hope months ago and was using a chromecast for netflix. Then last week, I thought I had a breakthrough. Out of boredom, I started googling my problem, and thought that maybe the devices weren't discovering the MTU properly. I turned on MSS clamping (iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu) (I also set it on the POSTROUTING chain on the mangle table). And when I turned on my devices, they both worked! I watched netflix all day on the blu ray player and the webcam was working.

A few days later, I was setting up xorg and had to recompile the kernel and restarted the server with the new kernel. I can't say for sure that the blu ray player was still working at this point (I hadn't tried it for a day or two), but it certainly wasn't working after the restart. I reloaded the old kernel, but to no avail. I made sure I applied the same settings I had tried before, but still no luck.

All other devices (a smart TV, a couple smart phones, etc.) work fine.

I hope someone here has some insight, because I am all out of ideas.

Thanks in advance!

I'll post more detail in my next comment
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chndrcks
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Joined: 27 Apr 2007
Posts: 4

PostPosted: Thu Dec 24, 2015 3:49 am    Post subject: Reply with quote

Some detail...

ip link:
Code:

plato ~ # ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: ethlan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether 6c:62:6d:c2:50:05 brd ff:ff:ff:ff:ff:ff
3: ethwan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether 00:0f:b5:8a:d7:e5 brd ff:ff:ff:ff:ff:ff
4: sit0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT group default
    link/sit 0.0.0.0 brd 0.0.0.0

ip addr
Code:

plato ~ # ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 brd 127.255.255.255 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: ethlan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 6c:62:6d:c2:50:05 brd ff:ff:ff:ff:ff:ff
    inet 10.0.1.1/24 brd 10.0.1.255 scope global ethlan
       valid_lft forever preferred_lft forever
    inet6 fe80::6e62:6dff:fec2:5005/64 scope link
       valid_lft forever preferred_lft forever
3: ethwan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:0f:b5:8a:d7:e5 brd ff:ff:ff:ff:ff:ff
    inet xxx.xxx.xxx.xxx/22 brd 255.255.255.255 scope global ethwan
       valid_lft forever preferred_lft forever
    inet6 fe80::f38e:44a9:7e91:d7b9/64 scope link
       valid_lft forever preferred_lft forever
4: sit0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN group default
    link/sit 0.0.0.0 brd 0.0.0.0


ip route
Code:
plato ~ # ip route
default via xxx.xxx.xxx.1 dev ethwan  metric 3
10.0.1.0/24 dev ethlan  proto kernel  scope link  src 10.0.1.1
xxx.xxx.xxx.0/22 dev ethwan  proto kernel  scope link  src xxx.xxx.xxx.xxx metric 3
127.0.0.0/8 dev lo  scope host


iptables-save
Code:
plato ~ # iptables-save
# Generated by iptables-save v1.4.21 on Wed Dec 23 21:48:10 2015
*security
:INPUT ACCEPT [473687759:632763080647]
:FORWARD ACCEPT [5362874309:5914488346290]
:OUTPUT ACCEPT [132545910:129842608329]
COMMIT
# Completed on Wed Dec 23 21:48:10 2015
# Generated by iptables-save v1.4.21 on Wed Dec 23 21:48:10 2015
*nat
:PREROUTING ACCEPT [1223:95908]
:INPUT ACCEPT [369:37614]
:OUTPUT ACCEPT [223:17056]
:POSTROUTING ACCEPT [223:17056]
-A POSTROUTING -s 10.0.1.0/24 -o ethwan -j MASQUERADE
-A POSTROUTING -s 10.0.2.0/24 -o ethwan -j MASQUERADE
COMMIT
# Completed on Wed Dec 23 21:48:10 2015
# Generated by iptables-save v1.4.21 on Wed Dec 23 21:48:10 2015
*mangle
:PREROUTING ACCEPT [8957:2275146]
:INPUT ACCEPT [866:64492]
:FORWARD ACCEPT [8084:2210358]
:OUTPUT ACCEPT [524:77201]
:POSTROUTING ACCEPT [8608:2287559]
-A FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
-A POSTROUTING -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
COMMIT
# Completed on Wed Dec 23 21:48:10 2015
# Generated by iptables-save v1.4.21 on Wed Dec 23 21:48:10 2015
*filter
:INPUT DROP [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [480:71077]
:logdrop - [0:0]
-A INPUT -i br0 -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -i ethlan -j ACCEPT
-A INPUT -p tcp -m tcp --dport 2222 -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -j DROP
-A FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
-A FORWARD -i br0 -j ACCEPT
-A FORWARD -i ethlan -j ACCEPT
-A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -j DROP
COMMIT
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