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I am having a weird problem which I cant figure out - so I was hoping someone here could give me a hand.

First off the end goal is that a specific server in my network runs an IPSEC connection to another company and I want all other servers to route traffic for the IP on that network through this single server.

Server 1 in this example is the server that runs the IPSEC connection. (CentOS 6.6)

Server 2 in this example is an app server that would route traffic for only that specific IP through server 1. (CentOS 6.5)

Some IP's that will be used below:

Server 1

Server 1 Public IP: x.x.x.x
Server 1 Public Broadcast: x.x.x.y
Server 1 Public Gateway: x.x.x.z
Server 1 Internal IP: 10.0.64.10/24

Server 2 

Server 2 Public IP: y.y.y.y
Server 2 Public Broadcast: y.y.y.z
Server 2 Public Gateway: y.y.y.a
Server 2 Internal IP: 10.0.64.150/24

Those servers have full connectivity between them internally (i.e. I can ping, ssh etc from one to the other without problem). They also both have full acceess to the internet and can be reached that way

Server 1

Here is an ip a for that 

# ip a
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0:  mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:99:12:85 brd ff:ff:ff:ff:ff:ff
    inet x.x.x.x/28 brd x.x.x.y scope global eth0
    inet6 xxxx:xxxx:xxxx:xxxx/64 scope link
       valid_lft forever preferred_lft forever
3: eth1:  mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:99:12:8f brd ff:ff:ff:ff:ff:ff
    inet 10.0.64.10/24 brd 10.0.64.255 scope global eth1
    inet6 fe80::20c:29ff:fe99:128f/64 scope link
       valid_lft forever preferred_lft forever

Here is an ip route

# ip route
x.x.x.y/28 dev eth0  proto kernel  scope link  src x.x.x.x
10.0.64.0/24 dev eth1  proto kernel  scope link  src 10.0.64.10
169.254.0.0/16 dev eth0  scope link  metric 1002
169.254.0.0/16 dev eth1  scope link  metric 1003
default via x.x.x.z dev eth0

Here is a sysctl -p

# sysctl -p
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
kernel.sysrq = 0
kernel.core_uses_pid = 1
net.ipv4.tcp_syncookies = 1
kernel.msgmnb = 65536
kernel.msgmax = 65536
kernel.shmmax = 68719476736
kernel.shmall = 4294967296
net.ipv4.ip_forward = 1
net.ipv6.conf.all.forwarding = 1
net.ipv4.conf.default.proxy_arp = 1
net.ipv4.conf.all.rp_filter = 1
kernel.sysrq = 1
net.ipv4.conf.default.send_redirects = 1
net.ipv4.conf.all.send_redirects = 1

Server 2

I've added a single test ip (8.8.8.8) to server two to test if it works before bringing IPSEC into the equation

Here is an ip a

# ip a
1: lo:  mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0:  mtu 1500 qdisc mq state UP qlen 1000
    link/ether 00:0c:29:15:8b:01 brd ff:ff:ff:ff:ff:ff
    inet y.y.y.y/29 brd y.y.y.z scope global eth0
    inet6 fe80::20c:29ff:fe15:8b01/64 scope link
       valid_lft forever preferred_lft forever
3: eth1:  mtu 1500 qdisc mq state UP qlen 1000
    link/ether 00:0c:29:15:8b:0b brd ff:ff:ff:ff:ff:ff
    inet 10.0.64.150/24 brd 10.0.64.255 scope global eth1
    inet6 fe80::20c:29ff:fe15:8b0b/64 scope link
       valid_lft forever preferred_lft forever

Here is an ip route

# ip route
8.8.8.8 via 10.0.64.10 dev eth1
y.y.y.z/29 dev eth0  proto kernel  scope link  src y.y.y.y
10.0.64.0/24 dev eth1  proto kernel  scope link  src 10.0.64.150
default via y.y.y.a dev eth0

Now when I try do a ping from Server 2 -> 8.8.8.8 here are the tcpdumps from each server:

Server 2

If I tcpdump on eth0 i get no matches (so the route appears right!). eth1 gets matches:

# tcpdump -vvv -i eth1 -n host 8.8.8.8
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
11:25:55.609902 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.0.64.150 > 8.8.8.8: ICMP echo request, id 17999, seq 1, length 64
11:25:56.609262 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.0.64.150 > 8.8.8.8: ICMP echo request, id 17999, seq 2, length 64

Server 1 (The hopeful gateway for 8.8.8.8)

On eth1 (Private)

# tcpdump -vv -i eth1 -n host 8.8.8.8
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes

11:27:20.608766 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.0.64.150 > 8.8.8.8: ICMP echo request, id 17999, seq 86, length 64
11:27:21.608738 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.0.64.150 > 8.8.8.8: ICMP echo request, id 17999, seq 87, length 64

On eth0 (public)

# tcpdump -vv -i eth0 -n host 8.8.8.8
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
11:29:04.608773 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.0.64.150 > 8.8.8.8: ICMP echo request, id 17999, seq 190, length 64
11:29:05.608800 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.0.64.150 > 8.8.8.8: ICMP echo request, id 17999, seq 191, length 64

I've disabled the FW on both (as a test), made sure to not have any blocking rules on FORWARD traffic (as a separate test) and I just never get my traffic through from Server 2 to 8.8.8.8. I've also tried substituting 8.8.8.8 for another server that is reachable from both servers and the same thing happens.

I'm open to any suggestions - i'm super confused :)

Thanks in advance, Ian

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1 Answer 1

Reset to default
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This is resolved!

I was missing the following rule in my IPTables ruleset: 

iptables -t nat -I POSTROUTING 1 -o eth0 --jump MASQUERADE
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