[PLUG] Baffled: CentOS 7 DHCP 10G fast, fixed 1G

Mike C. mconnors1 at gmail.com
Thu Nov 14 18:22:24 UTC 2019


 "I am baffled. I have a Centos 7 system with a 10GbE Intel adapter
that works consistently at 10GbE when configured with DHCP. With a
fixed address... I get 1GbE. Every time."

Are you saying "automatic" network configuration via DHCP verses "manual"
configuration via a human being?

I say this because you can you use DHCP to configure all the network
settings for a client but it can still have a fixed ip address per DHCP
reservation but all the other network settings would be preserved.

"There are two NICs on the same subnet as not to get locked out. Some OSs
tolerate this while some do not. Because "dhclient" addressing works fine,
I trust that is okay but the plan is to next try it without the 1GbE
interface connected."

Is this TWO 10 GB NICs in which you have 1 port configured via DHCP and 1
port configured via a static IP address and manual network configuration?

If so, this should be an either or problem:

Either the static ip addressed nic port isn't configured for
auto-negotiation. In which case you can use Ethtool to determine that and
correct it.
https://www.shellhacks.com/change-speed-duplex-ethernet-card-linux/

Or the connection on the other end isn't a 10 GB capable port, isn't
configured for auto-negotiate or there's a physical cable (damage, length)
or NIC problem that is causing auto-negotiate to determine the link can't
support 10 GB and is knocking it down to 1 GB/s.

If you've got ONE 1 GB and ONE 10 GB port and the 1 GB is statically ip
addressed then you can change the default admin routing cost of the
interface from 1 to 255.  That will assure the 10 GB handles all the
traffic unless that link fails.

The route command will show the metric of each route. Lowest metric route
is used first.

route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use
Iface
0.0.0.0         192.168.43.51   0.0.0.0         UG    600    0        0
wlp2s0b1
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0
wlp2s0b1
192.168.43.0    0.0.0.0         255.255.255.0   U     600    0        0
wlp2s0b1

So if you've got a statically assigned ip address and route on the 1 GB
interface, here's how you'd change the metric from 1 to 255.

sudo route add -net default gw 10.10.0.1 netmask 0.0.0.0 dev wlan0 metric 1


I hope that's all somewhat clear and helpful.

-- Mike



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