How to build routes correctly?

Question

linux

There is a network 172.16.100.0/24 which needs to be given access to the Internet through the ens19 interface, its address is 10.0.88.111/24, the gateway is 10.0.88.254, I wrote the following:

default via 10.0.88.254 dev ens19
ip route add 172.16.100.0/24 via 10.0.88.111
iptables -A POSTROUTING -t nat -s 172.16.100.0/24 -o ens19 -j MASQUERADE

Forwarding is enabled, but packets are not visible when sniffing, there is Internet with ens19, what could be the problem?

Answer 1

Try like this:

echo > /etc/iproute2/rt_tables 200 ens19
ip rule add from 172.16.100.0/24 lookup ens19
ip route add default via 10.0.88.254 table ens19
iptables -A POSTROUTING -t nat -s 172.16.100.0/24 -o ens19 -j MASQUERADE

echo > /etc/iproute2/rt_tables 200 ens19 - create new ens19 routing table with priority 200
ip rule add from 172.16.100.0/24 lookup ens19 - create new routing rule where packets from 172.16.100.0/24 are routed through ens19
ip table route add default via 10.0.88.254 table ens19 - add default route to ens19 table
iptables -A POSTROUTING -t nat -s 172.16.100.0/24 -o ens19 -j MASQUERADE - packet masquerading
This should work.

Answer 2

what's in FORWARD? (iptables -L FORWARD -vnx)

Answer 3

You spelled it wrong.
The 172.16.100.0/24 network does not need to know anything about "ens19 interface, its address is 10.0.88.111/24, the gateway is 10.0.88.254"
For it, only an address from its own subnet can be a gateway, so this entry "ip route add 172.16. 100.0/24 via 10.0.88.111" is fundamentally wrong.
Describe the interfaces on the server in more detail.