Hooking Linux machine to secondary router/ISP: how to setup routing correctly?

Abstract:

I have (I presume routing) issues when adding a secondary ISP to my existing network setup: incoming traffic through Router1 is not answered, but local traffic and incoming through Router0 is working fine.

How can I keep the parts that currently function well working, while making incoming traffic through Router1 work?

Elaboration:

I've sketched a diagram below with the bare essentials of the situation (in practice there are more devices on each LAN, but they do not matter).

This is the situation:

• I have two internal networks: LAN0 is 192.168.x.0/24 and LAN1 is 192.168.y.0/24. Both work fine for internal traffic (for instance http using cURL).
• LAN0 has always been connected through Router0 and ISP0 to the Internet.
• LAN1 always had Router1, but is now connected through ISP1 to the Internet.
• Machines only on LAN0 and having a default route through Router0 work fine for outgoing and incoming traffic.
• Machines only on LAN1 and having a default route through Router1 work fine for outgoing and incoming traffic.
• Internal traffic on LAN0 and LAN1 has always worked fine.
• Incoming traffic through Router1 for WindowsB arrives correctly: I can connect to it over RDP from WindowsC.
• Incoming traffic through Router1 for LinuxB arrives (according to tcpdump), but not answered back as a curl http://e.f.g.h fron LinuxC shows with a tcpdump onLinuxB shows:

It shows only packets that - according to the tcpdump output format - have a SYN flag set:

LinuxB:/tmp/LinuxB.eth1.80 # tcpdump -i eth1 'port 80'tcpdump: verbose output suppressed, use -v or -vv for full protocol decodelistening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes13:35:19.489779 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,nop,wscale 4,nop,nop,TS val 1287047182 ecr 0,sackOK,eol], length 013:35:19.788841 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,nop,wscale 4,nop,nop,TS val 1287047478 ecr 0,sackOK,eol], length 013:35:19.888835 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,nop,wscale 4,nop,nop,TS val 1287047578 ecr 0,sackOK,eol], length 013:35:19.989412 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,nop,wscale 4,nop,nop,TS val 1287047678 ecr 0,sackOK,eol], length 013:35:20.089685 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,nop,wscale 4,nop,nop,TS val 1287047778 ecr 0,sackOK,eol], length 013:35:20.190836 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,nop,wscale 4,nop,nop,TS val 1287047877 ecr 0,sackOK,eol], length 013:35:20.392123 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,nop,wscale 4,nop,nop,TS val 1287048072 ecr 0,sackOK,eol], length 013:35:20.693692 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,sackOK,eol], length 013:35:21.197162 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,sackOK,eol], length 013:35:22.204134 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,sackOK,eol], length 013:35:24.115961 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,sackOK,eol], length 013:35:27.852374 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,sackOK,eol], length 013:35:31.967049 IP i.j.k.l.57512 > 192.168.y.2.http: Flags [S], seq 816356596, win 65535, options [mss 1460,sackOK,eol], length 0

This is the LinuxB route table:

LinuxB:/tmp/LinuxB.eth1.80 # routeKernel IP routing tableDestination     Gateway         Genmask         Flags Metric Ref    Use Ifacedefault         192.168.x.1     0.0.0.0         UG    0      0        0 eth0loopback        *               255.0.0.0       U     0      0        0 lolink-local      *               255.255.0.0     U     0      0        0 eth0192.168.x.0     *               255.255.255.0   U     0      0        0 eth0192.168.x.0     *               255.255.255.0   U     0      0        0 eth1

Since connecting over RDP from WindowsC to WindowsB works fine, I resume this is indeed a routing problem. This is the WindowsB route table:

C:\temp>route print===========================================================================Interface List0x1 ........................... MS TCP Loopback interface0x2 ...00 0c 29 35 77 e1 ...... AMD PCNET Family PCI Ethernet Adapter - Packet Scheduler Miniport0x3 ...00 0c 29 35 77 eb ...... VMware Accelerated AMD PCNet Adapter - Packet Scheduler Miniport======================================================================================================================================================Active Routes:Network Destination        Netmask          Gateway       Interface  Metric          0.0.0.0          0.0.0.0      192.168.x.1     192.168.x.4      10          0.0.0.0          0.0.0.0      192.168.y.1     192.168.y.4       5        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1      192.168.x.0    255.255.255.0      192.168.x.4     192.168.x.4      10      192.168.x.4  255.255.255.255        127.0.0.1       127.0.0.1      10    192.168.x.255  255.255.255.255      192.168.x.4     192.168.x.4      10      192.168.y.0    255.255.255.0      192.168.y.4     192.168.y.4      10      192.168.y.4  255.255.255.255        127.0.0.1       127.0.0.1      10    192.168.y.255  255.255.255.255      192.168.y.4     192.168.y.4      10        224.0.0.0        240.0.0.0      192.168.x.4     192.168.x.4      10        224.0.0.0        240.0.0.0      192.168.y.4     192.168.y.4      10  255.255.255.255  255.255.255.255      192.168.x.4     192.168.x.4       1  255.255.255.255  255.255.255.255      192.168.y.4     192.168.y.4       1Default Gateway:       192.168.y.1===========================================================================Persistent Routes:  Network Address          Netmask  Gateway Address  Metric          0.0.0.0          0.0.0.0      192.168.y.1       5          0.0.0.0          0.0.0.0      192.168.x.1      10

So how can I get the routing on LinuxB to be like this:

• keep default route on LinuxB to 192.168.x.1 so outgoing traffic keeps using Router0/ISP0
• keep answering incoming requests coming from LAN0 on LAN0
• keep answering incoming requests coming from LAN1 on LAN1
• keep answering incoming requests through Router0 (a.b.c.d/192.168.x.1) via 192.168.x.1
• start answering incoming requests through Router1 (e.f.g.h/192.168.y.1) via 192.168.y.1
• bonus: have Router1 fail-over or load-balance with Router0

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