Access VM from LAN

Question

On a Linux laptop, I want to give access to locally hosted VM (kvm) from LAN.

I'd like to do DNAT to VM.

Network

client  <-- LAN 192.168.3.0/24 --> host <-- bridge 192.168.113.0/24 --> guest

Host

• wlp3s0: 192.168.3.221/24
• br0: 192.168.113.1/24
• net.ipv4.ip_forward = 1
• Bridge:

# bridge -d link
16: vnet5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master br0 state forwarding priority 32 cost 100 
    hairpin off guard off root_block off fastleave off learning on flood on mcast_flood on bcast_flood on mcast_router 1 mcast_to_unicast off neigh_suppress off vlan_tunnel off isolated off locked off

• Routing:

default via 192.168.3.1 dev wlp3s0 proto dhcp src 192.168.3.221 metric 600 
192.168.3.0/24 dev wlp3s0 proto kernel scope link src 192.168.3.221 metric 600 
192.168.113.0/24 dev br0

• Netfilter rule extract:

table inet filter {
  chain forward {
    type filter hook forward priority 0; policy drop;
    ct state established,related counter accept
    ct state invalid counter drop
    tcp dport 8080 counter log prefix "forward: " accept
  }
}

table ip nat {
  chain prerouting {
    type nat hook prerouting priority dstnat
    tcp dport 8080 counter log prefix "dnat: " dnat to 193.168.113.201:8080
  }
  chain postrouting {
    type nat hook postrouting priority srcnat
    iifname br0 oifname wlp3s0 counter masquerade
  }
}

Guest

• enp1s0: 192.168.113.201/24
• Routes:

default via 192.168.113.1 dev enp1s0 proto dhcp src 192.168.113.201 metric 100 
192.168.113.0/24 dev enp1s0 proto kernel scope link src 192.168.113.201 metric 100

• No firewall
• Service listening on 0.0.0.0:8080

Client

• address: 192.168.3.2

Tests OK

• Ping from host to guest (ping -c 1 192.168.113.201)
• Curl from host to guest service (curl -q http://192.168.113.201:8080)
• Access to internet from guest (curl -q https://serverfault.com)

Issue

Calling service from another client on LAN (curl -q http://192.168.3.221:8080) does not reach the guest.

Tcpdump on wlp3s0 interface of the host:

11:10:54.063354 IP 192.168.3.2.43278 > 192.168.3.221.8080: Flags [S], seq 2985774913, win 64240, options [mss 1460,sackOK,TS val 525180874 ecr 0,nop,wscale 7], length 0
11:10:54.063388 IP 192.168.3.2.43278 > 193.168.113.201.8080: Flags [S], seq 2985774913, win 64240, options [mss 1460,sackOK,TS val 525180874 ecr 0,nop,wscale 7], length 0

(I see "forward" and "dnat" lines in syslog when forwarding and filtering are triggered.)

I see no packet on br0 interface of the host.

Please note the second line of tcpdump. Destination is rewritten, but on the wlp3s0 interface!

I also tested with wired Ethernet instead of Wifi: exactly same behavior.

Why the packet is not routed to bridge through br0?

Any hint appreciated!

Answer 1

There is a typo in the prerouting rule. dnat to 193.168.113.201:8080 instead of dnat to 192.168.113.201:8080.