I replaced my consumer wireless router with a linux box that has a quad-gigabit NIC PCIe card and a single gigabit NIC on the motherboard (for the WAN). After turning on IP forwarding, masquerading (via iptables), and setting up subnets on each of the four LAN interfaces I ran some speed tests.
$ ip route
default dev ppp0 scope link
10.0.0.0/16 dev enp3s0f0 proto kernel scope link src 10.0.0.1
10.64.0.0/16 dev enp3s0f1 proto kernel scope link src 10.64.0.1
10.192.0.0/16 dev enp4s0f1 proto kernel scope link src 10.192.0.1
aaa.bbb.ccc.ddd dev ppp0 proto kernel scope link src www.xxx.yyy.zzz
From a wireless device on one of the LAN subnets to a speedtest server on the WAN I get the full 40 Mbps / 5 Mbps I pay my ISP for.
From the router host to a wired LAN host using
iperf3I can consistently maintain 930+ Mbps for several minutes.From a wired device on one of the LAN subnets to a wired device on a different LAN subnet using
iperf3I initially get 80-95 Mbps for the first few seconds but it rapidly drops to zero.From a wired device on one of the LAN subnets to a wired device on a different LAN subnet using
iperf3with a target bitrate of 20 Mbps I see the similar results (see update at end), but can sustain about 10 Mpbs
.
Connecting to host 10.0.0.2, port 5201
[ 5] local 10.192.128.3 port 35620 connected to 10.0.0.2 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 10.2 MBytes 85.9 Mbits/sec 0 73.5 KBytes
[ 5] 1.00-2.00 sec 9.01 MBytes 75.6 Mbits/sec 0 82.0 KBytes
[ 5] 2.00-3.00 sec 8.26 MBytes 69.3 Mbits/sec 0 79.2 KBytes
[ 5] 3.00-4.00 sec 9.01 MBytes 75.6 Mbits/sec 0 73.5 KBytes
[ 5] 4.00-5.00 sec 5.28 MBytes 44.3 Mbits/sec 1 1.41 KBytes
[ 5] 5.00-6.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
[ 5] 6.00-7.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
[ 5] 7.00-8.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
[ 5] 8.00-9.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
^C[ 5] 10.00-13.63 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-13.63 sec 41.8 MBytes 25.7 Mbits/sec 5 sender
[ 5] 0.00-13.63 sec 0.00 Bytes 0.00 bits/sec receiver
iperf3: interrupt - the client has terminated
This is suggesting to me that there's some problem forwarding packets between the subnets. I first ensured that my iptables rules are as minimal as possible:
-t nat -A POSTROUTING -o ppp0 -j MASQUERADE
# WAN connection is PPPoE and VLAN tagged
-t filter -A FORWARD -o ppp0 -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
Dumping the iptables state I see low packet counts for both rules.
Next I checked for packet loss. There does seem to be a small but consistent amount of packet loss / retransmits.
$ sudo netstat -s | egrep -i 'retransmit|drop'
498 outgoing packets dropped
25848 fast retransmits
I then thought that maybe there was a buffer or queue that was filling and packets were getting dropped. I calculated the average bandwidth-delay product and compared that against the reserved memory.
$ sudo ping -f 10.0.0.2 -s $((1500-28))
PING 10.0.0.2 (10.0.0.2) 1472(1500) bytes of data.
.^C
--- 10.0.0.2 ping statistics ---
9036 packets transmitted, 9035 received, 0% packet loss, time 26512ms
rtt min/avg/max/mdev = 1.742/2.817/12.057/0.758 ms, pipe 2, ipg/ewma 2.934/3.091 ms
$ echo "1*(1024^3) * 0.003" | bc
3221225.472
$ cat /proc/sys/net/ipv4/tcp_mem
18396 24529 36792
$ getconf PAGESIZE
4096
That appears to be sufficient. So now I'm a bit stuck. I ran tcpdump on the iperf3 client and can see things moving along well for a bit. Then I see a long (almost 250ms) period of silence before lots of retransmits and duplicate acknowledgements.
Since I can pull sufficient download speeds from the WAN I don't suspect that the onboard NIC is at fault. I'm looking for help to diagnose this quad-NIC (details below) and possibly a dumb layer-2 gigabit switch (Netgear GS-108) and any other kernel configuration that could be getting in the way. I doubt it's the switch, as it's never been a problem before and I can maintain speeds from the router's loopback to that subnet. Only inter-subnet performance appears to be affected.
*-network:0
description: Ethernet interface
product: 82571EB Gigabit Ethernet Controller (Copper)
vendor: Intel Corporation
physical id: 0
bus info: pci@0000:03:00.0
logical name: enp3s0f0
version: 06
serial: 00:26:55:xx:xx:xx
size: 1Gbit/s
capacity: 1Gbit/s
width: 32 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=3.2.6-k duplex=full firmware=5.12-2 ip=10.0.0.1 latency=0 link=yes multicast=yes port=twisted pair speed=1Gbit/s
resources: irq:24 memory:fe920000-fe93ffff memory:fe880000-fe8fffff ioport:d020(size=32)
UPDATE:
$ iperf3 -b 20m -c 10.0.0.2
Connecting to host 10.0.0.2, port 5201
[ 5] local 10.192.128.3 port 36554 connected to 10.0.0.2 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 2.49 MBytes 20.9 Mbits/sec 0 158 KBytes
[ 5] 1.00-2.00 sec 2.38 MBytes 19.9 Mbits/sec 0 150 KBytes
[ 5] 2.00-3.00 sec 2.38 MBytes 19.9 Mbits/sec 1 133 KBytes
[ 5] 3.00-4.00 sec 2.38 MBytes 19.9 Mbits/sec 0 73.5 KBytes
[ 5] 4.00-5.00 sec 2.38 MBytes 19.9 Mbits/sec 0 70.7 KBytes
[ 5] 5.00-6.00 sec 1.12 MBytes 9.44 Mbits/sec 2 1.41 KBytes
[ 5] 6.00-7.00 sec 0.00 Bytes 0.00 bits/sec 2 1.41 KBytes
[ 5] 7.00-8.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 8.00-9.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
iperf3: error - control socket has closed unexpectedly
$ iperf3 -b 10m -c 10.0.0.2
Connecting to host 10.0.0.2, port 5201
[ 5] local 10.192.128.3 port 36564 connected to 10.0.0.2 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 1.24 MBytes 10.4 Mbits/sec 0 201 KBytes
[ 5] 1.00-2.00 sec 1.25 MBytes 10.5 Mbits/sec 0 118 KBytes
[ 5] 2.00-3.00 sec 1.12 MBytes 9.44 Mbits/sec 0 127 KBytes
[ 5] 3.00-4.00 sec 1.25 MBytes 10.5 Mbits/sec 0 107 KBytes
[ 5] 4.00-5.00 sec 1.12 MBytes 9.44 Mbits/sec 0 110 KBytes
[ 5] 5.00-6.00 sec 1.25 MBytes 10.5 Mbits/sec 0 90.0 KBytes
[ 5] 6.00-7.00 sec 1.12 MBytes 9.44 Mbits/sec 0 87.2 KBytes
[ 5] 7.00-8.00 sec 1.25 MBytes 10.5 Mbits/sec 0 81.6 KBytes
[ 5] 8.00-9.00 sec 1.12 MBytes 9.44 Mbits/sec 0 78.8 KBytes
[ 5] 9.00-10.00 sec 1.25 MBytes 10.5 Mbits/sec 0 112 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 12.0 MBytes 10.1 Mbits/sec 0 sender
[ 5] 0.00-10.04 sec 12.0 MBytes 10.0 Mbits/sec receiver
iperf Done.
ifconfig -aorip addr. Looking for mac addresses on the quad NIC.