0

This is in my router's routing table:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 br0

And this is my host's routing table:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1        0.0.0.0         UG    100    0        0 enp0s3
192.168.1.0        0.0.0.0         255.255.255.0   U     100    0        0 enp0s3

and here is the br0 interface of the router:

br0       Link encap:Ethernet  HWaddr 24:4B:FE:F0:18:C0  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING ALLMULTI MULTICAST  MTU:1500  Metric:1
          RX packets:68370 errors:0 dropped:0 overruns:0 frame:0
          TX packets:82681 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:7411859 (7.0 MiB)  TX bytes:64534493 (61.5 MiB)

How would two hosts in the 192.168.1 subnet communicate with eachother? If they were both only connected to the router with ethernet? Here's how i think it works:

  1. host at 192.168.1.10 wants to send to 192.168.1.11
  2. The routing table entry 192.168.1.0 is chosen
  3. the host will broadcast an arp request for the mac address of 1.11
  4. The router receives this arp request on its br0 interface
  5. The bridge interface gets the mac address of 1.11 and sends it back to 1.10?
  6. The 1.10 host sends a frame with the mac address of 1.11 to the router's br0 interface?
  7. So does the bridge interface now realize that the mac address is not its own, and then forwards it to the correct host?
5
  • ARP is replied to by the node 'owning' that IP address, not some router (unless the address belongs to that router).
    – Zac67
    Dec 19, 2022 at 13:38
  • @Zac67 ok, does the bridge interface look at the ip header at all? Dec 19, 2022 at 13:42
  • You are confusing routers and bridges. Bridges/switches work on the data link layer (MAC addresses) only and are completely agnostic to the network layer, IP addresses and such.
    – Zac67
    Dec 19, 2022 at 13:46
  • 1
    As mentioned, 2 hosts on a network must be connected by a bridge or switch (otherwise they are not on the same network). If they are connected via a router, then they are on 2 different networks with a router between them. When they are on the same network, ARP helps them find each other via broadcast. Remember that a typical home/small office router will usually include a built in 4 (or more) port switch to facilitate this functionality. Some routers may reply to ARP for other hosts if they have that functionality enabled (Proxy ARP) but that is a separate thing. Dec 19, 2022 at 15:33
  • You are referring to a (off-topic) consumer-grade "router" that is really a Frankenstein box with a router, NAT, DHCP, switch, Wi-Fi, etc. all rolled into a single chassis. The devices communicating on the same network use the switch (bridge) and/or Wi-Fi (bridge) and do not pass through the router part of the device.
    – Ron Maupin
    Dec 19, 2022 at 19:20

0