Unwanted route on Synology router

[Nermal]

Hi everyone,

I have a Synology RT6600ax router and I'm having an unusual (at least to my eyes) problem. I'm connecting to my ISP using DHCP (IPoE) and my IPv4 address is in the 118.67.x.x range.

The problem is that I can't connect to any websites or other public servers in the 118.x.x.x range. For example:

% traceroute www.gog.com
traceroute to e11072.b.akamaiedge.net (118.215.88.211), 64 hops max, 40 byte packets
 1  10.0.1.1 (10.0.1.1)  0.763 ms  0.440 ms  0.335 ms
 2  my-public-ip.rdns-s.quic.net.nz (my.public.ip)  2993.909 ms !H  2990.678 ms !H  2999.823 ms !H

In SRM if I go to Network Centre/Local Network/Static Route/IP Routing Table, there's an entry in there with the following settings:
Network destination: 118.0.0.0
Gateway: 0.0.0.0
Netmask: 255.0.0.0

If I'm understanding this correctly then it seems that the router thinks everything in 118.0.0.0/8 is on my local network and therefore requests don't actually hit my Internet connection.

Does anyone know how I can change this entry and tell the router that it should only be my single IPv4 address, not the entire /8?

Interestingly if I change from DHCP to PPPoE then the rogue entry either disappears or changes to the single address (I didn't take a screenshot and I don't fancy changing it back), and everything then works as expected, so I do have a workaround, but it would be nice to get everything working over DHCP if I can.

Any ideas?

 

[Bigwaff]

The WAN IP is within ISP IP range. Your LAN IP range is router default or have you customized it?

 

[Nermal]

I changed the LAN range from the default (class C) to 10.0.1.0/24, so as to match what my old AirPort was doing. I never thought to look at those particular settings so I'll double-check them.

 

[Nermal]

There aren't really any relevant settings in there. "Local IP" (i.e. the address of the router) is set to 10.0.1.1, subnet mask is 255.255.255.0. The IPv4 DHCP range is 10.0.1.2 through 10.0.1.200. Nothing seems to be "spilling out" of the subnet that I can see.

 

[Bigwaff]

Basics look good. Perhaps your router config or your ISP’s equipment is set to drop or ignore ICMP packets.

 

[Nermal]

I've just done a factory reset (so it's back on 192.168.1.0/24) and right out of the box that 118.0.0.0/8 route is still there.

 

[Weaselboy]

I am on the Synology 2600, but same firmware, and mine shows nothing in that pane. What happens if you just remove that entry?

 

[Nermal]

Click on "IP Routing Table". You can't remove entries from that window.

 

[Nermal]

I've been discussing this on another forum and the consensus seems to be that it's a Synology bug. My ISP's DHCP server is providing my IP address along with a subnet mask of 255.255.255.255, and it seems that the router is treating it like it's 255.0.0.0. Apparently most ISPs use 255.255.255.252, and .255 is apparently a rarity.

 

[Nermal]

I've given up and switched back to PPPoE. This is turn has broken IPv6 for reasons as yet unknown, but given that virtually everything is v4-compatible I'd rather give up v6 than give up a 254th of the Internet.

 

[Nermal]

I ended up contacting Synology support and they confirmed that it's a bug and gave me a firmware update. Presumably it'll be rolled into the public firmware at some point.