IP route on DHCP client

[Virivé Fabio]

Hi everibody,
I have an Armbian 25.2.3 bookworm fresh installed and I have some problem with IP route.

In my network there is an DHCP server that serve the IP address and route to the client.
The server is _isc-dhcpd-4.1.1-P1_.
In my network there are multiple OS like Debian 12, ArchLinux, MacOS and Windows, 
all the clients get the IP configurations via DHCP without problems.

The issue is reported only on the Armbian client and it concerns the configuration of the IP route.
In the Armbian device is not created the default route and there are two IP route that not be exist and are also wrong. 
In the DHCP server I have the configuration for serve the default route and other additional route, option 121.
The IP routes served via option 121 are present but the default route no.
Furthermore there are two route about DNS that not be exist and if I delete it, these routes appear again soon.

This is the output of `ip route`:
 

**1.1.1.1 dev wlx012ab3456789 proto dhcp scope link src 10.X.X.100 metric 600** 
**8.8.4.4 dev wlx012ab3456789 proto dhcp scope link src 10.X.X.100 metric 600** 
X.0.0.0/24 via 10.x.x.10 dev wlx012ab3456789 proto dhcp src 10.X.X.100 metric 600 
10.X.X.0/24 dev wlx012ab3456789 proto kernel scope link src 10.X.X.100 metric 600 
10.x.x.10 dev wlx012ab3456789 proto dhcp scope link src 10.X.X.100 metric 600 
10.y.0.0/24 via 10.x.x.10 dev wlx012ab3456789 proto dhcp src 10.X.X.100 metric 600 
10.x.x.0/24 via 10.x.x.10 dev wlx012ab3456789 proto dhcp src 10.X.X.100 metric 600 
192.z.0.0/24 via 10.x.x.10 dev wlx012ab3456789 proto dhcp src 10.X.X.100 metric 600

 

As you can see there is no _default route_ and exists two route about DNS host that are also wrong.
Even if I put the default route manually the two routes about DNS server host prevent it to be reached, so I must remove these two routes manually, but these two route appear again after few minutes. 

If I sniff the traffic during the DHCP request, the response is ok:
 

17:35:07.031609 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 353)
    10.x.x.10.67 > 10.x.x.100.68: BOOTP/DHCP, Reply, length 325, xid 0x67291d40, secs 1499, Flags [none]
          Client-IP 10.x.x.100
          Your-IP 10.x.x.100
          Server-IP 10.x.x.10
          Client-Ethernet-Address 01:2a:b3:45:67:89
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: ACK
            Server-ID (54), length 4: 10.x.x.10
            Lease-Time (51), length 4: 600
            Subnet-Mask (1), length 4: 255.255.255.0
            Default-Gateway (3), length 4: 10.x.x.1
            Domain-Name-Server (6), length 8: 1.1.1.1,8.8.4.4
            Domain-Name (15), length 11: "dnsname.lan"
            Classless-Static-Route (121), length 32: (10.x.x.0/24:10.x.x.10),(192.z.0.0/24:10.x.x.10),(x.0.0.0/24:10.x.x.10),(10.y.0.0
/24:10.x.x.10)

 

How can I fix it?

Edited yesterday at 07:26 AM by Virivé Fabio

[IBV]

Hi,

 

take a look at this similar issue:

https://forums.raspberrypi.com/viewtopic.php?t=306463

 

Accroding to the RFC, the behaviour you see is correct, when Classless-Static-Route (121) is offered, the router option (3) must be ignored.