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Thread: Routing problems with two interfaces

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  1. #1
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    Routing problems with two interfaces

    I run a small, low power machine with two interfaces as a file and torrent server. Both interfaces are on the same LAN. I typically assign different services to different interfaces, such as AFP, SMB, SSH to one and the Azureus to the other. This has worked fine in 8.04 but with 10.04 if I bring up the machine with both interfaces active packets cannot find their way back through my firewall (LAN traffic is fine). A traceroute stops right at my firewall. This is not exclusive to my network environment, either- I've tested with a virtual machine at work as well and packets cannot find their way back beyond the first router. I'm not the best at troubleshooting but the basic network issues so I'm at a loss what occurred between 8.04 and 10.04 that is causing this problem.

  2. #2
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    Ubuntu 11.04 Natty Narwhal

    Re: Routing problems with two interfaces

    Your network layout is not clear. Is your "firewall" the same machine.

  3. #3
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    Re: Routing problems with two interfaces

    No, this is a single machine behind a firewall which is another machine. There is no firewall software running on the server unless there is something preconfigured that I do not know about. This is the same configuration that is running on the virtual machine that I have tested in other environments. I invite you to attempt the same configuration using VirtualBox with a server install (not desktop).

  4. #4
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    Re: Routing problems with two interfaces

    For argument's sake, I created a default install of Debian 5.0.4 in a virtual machine and there is no problem with two interfaces and package routing. The kernel is off by several versions, however (2.6.26), assuming that this could be at all kernel related.

    Edit:
    I updated to the most recent backported kernel in Debian 5.0.4, 2.6.32-bpo.5, and this issue does not exist. It seems Ubuntu isolated.
    Last edited by sonicbuddha; July 22nd, 2010 at 10:59 AM.

  5. #5
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    Re: Routing problems with two interfaces

    Turn off sending and listening to ICMP redirects, if that does not fix it post your routing table. It could very well be that you have two default routes. If that is case, just delete one of them and prevent its recurrence by configuring the interfaces in /etc/network/interfaces so that you can control which interface is going to get the gateway.

  6. #6
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    Re: Routing problems with two interfaces

    I'll try turning off sending and listening to ICMP redirects but having two default routes should not be a problem- and isn't a problem for 8.04, my Debian test install, or any other operating system I've tested with (OS X, Windows). For not specific traffic it simply picks up the first default and for applications bound to specific applications they use the first default they can- the address they are bound to. 10.04 is the only install I've ever had that choked with more than one default route (thus the post).

  7. #7
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    Ubuntu 11.04 Natty Narwhal

    Re: Routing problems with two interfaces

    Quote Originally Posted by sonicbuddha View Post
    For argument's sake, I created a default install of Debian 5.0.4 in a virtual machine and there is no problem with two interfaces and package routing. The kernel is off by several versions, however (2.6.26), assuming that this could be at all kernel related.

    Edit:
    I updated to the most recent backported kernel in Debian 5.0.4, 2.6.32-bpo.5, and this issue does not exist. It seems Ubuntu isolated.
    Let me see the routing table for this and the output from ifconfig, just to make sure we are the same page.

  8. #8
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    Re: Routing problems with two interfaces

    If we can, I'd like to move away from discussing why the question was asked and instead focus on answering the question itself, please. Something is different in 10.04 and even if the purpose may not be applicable in a particular environment, the result still remains interesting, worthwhile, and, in fact, may apply in ways not otherwise immediately evident. I am really hoping there is a security protocol, kernel setting, or service running that was implemented somewhere between 8.04 and 10.04 that can be identified, if not managed.

    As for proof of concept, here are the ifconfig and route values from installs where two interfaces with the same gateway works, 8.04, Debian 5.04, OS X 10.6.4, and Open Solaris 9, and a non-working 10.04. I just created a default 9.10 install and this 'problem' exists here, too. Note that Open Solaris and OS X do not have a 'route' command that returns routing like Linux, so I used netstat -nr

    Working 8.04 configuration:
    eth0 Link encap:Ethernet HWaddr 00:30:18:ad:ed:ec
    inet addr:10.1.1.15 Bcast:10.1.1.255 Mask:255.255.255.0
    inet6 addr: fe80::230:18ff:fead:edec/64 Scope:Link
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:26595768 errors:0 dropped:0 overruns:0 frame:0
    TX packets:12716759 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000
    RX bytes:3427873578 (3.1 GB) TX bytes:3744703590 (3.4 GB)
    Interrupt:16

    eth1 Link encap:Ethernet HWaddr 00:30:18:ad:ed:ed
    inet addr:10.1.1.16 Bcast:10.1.1.255 Mask:255.255.255.0
    inet6 addr: fe80::230:18ff:fead:eded/64 Scope:Link
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:27604069 errors:0 dropped:0 overruns:0 frame:0
    TX packets:54302172 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000
    RX bytes:4183963946 (3.8 GB) TX bytes:1736026744 (1.6 GB)
    Interrupt:17 Base address:0x2000


    Kernel IP routing table
    Destination Gateway Genmask Flags Metric Ref Use Iface
    10.1.1.0 * 255.255.255.0 U 0 0 0 eth0
    10.1.1.0 * 255.255.255.0 U 0 0 0 eth1
    default blackbox.xxxx 0.0.0.0 UG 100 0 0 eth1
    default blackbox.xxxx 0.0.0.0 UG 100 0 0 eth0

    Debian 5.0.4
    eth0 Link encap:Ethernet HWaddr 00:0c:29:87:c0:5d
    inet addr:10.1.1.133 Bcast:10.1.1.255 Mask:255.255.255.0
    inet6 addr: fe80::20c:29ff:fe87:c05d/64 Scope:Link
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:300 errors:0 dropped:0 overruns:0 frame:0
    TX packets:68 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000
    RX bytes:32228 (31.4 KiB) TX bytes:4072 (3.9 KiB)
    Interrupt:19 Base address:0x2000

    eth1 Link encap:Ethernet HWaddr 00:0c:29:87:c0:67
    inet addr:10.1.1.109 Bcast:10.1.1.255 Mask:255.255.255.0
    inet6 addr: fe80::20c:29ff:fe87:c067/64 Scope:Link
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:5285 errors:0 dropped:0 overruns:0 frame:0
    TX packets:3319 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000
    RX bytes:7677393 (7.3 MiB) TX bytes:248631 (242.8 KiB)
    Interrupt:19 Base address:0x2080


    Destination Gateway Genmask Flags Metric Ref Use Iface
    10.1.1.0 * 255.255.255.0 U 0 0 0 eth1
    10.1.1.0 * 255.255.255.0 U 0 0 0 eth0
    default blackbox.xxxx 0.0.0.0 UG 0 0 0 eth0
    default blackbox.xxxx 0.0.0.0 UG 0 0 0 eth1

    OS X 10.6.4
    en0: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMP LEX,MULTICAST> mtu 1500
    ether 00:1f:5b:32:37:88
    inet6 fe80::21f:5bff:fe32:3788%en0 prefixlen 64 scopeid 0x4
    inet 10.1.1.100 netmask 0xffffff00 broadcast 10.1.1.255
    media: autoselect (1000baseT <full-duplex,flow-control>)
    status: active
    en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULT ICAST> mtu 1500
    ether 00:1f:5b:32:37:89
    inet6 fe80::21f:5bff:fe32:3789%en1 prefixlen 64 scopeid 0x5
    inet 10.1.1.157 netmask 0xffffff00 broadcast 10.1.1.255
    media: autoselect (1000baseT <full-duplex,flow-control>)
    status: active
    netstat -nr
    Routing tables

    Internet:
    Destination Gateway Flags Refs Use Netif Expire
    default 10.1.1.1 UGSc 12 0 en0
    default 10.1.1.1 UGScI 0 0 en1
    10.1.1/24 link#4 UCS 13 0 en0
    10.1.1/24 link#5 UCSI 1 0 en1
    10.1.1.1 0:18:f8:77:a0:3f UHLWI 6 74 en0 1167
    10.1.1.11 0:1a:92:b9:e2:1 UHLWI 1 6 en0 1169
    10.1.1.14 link#4 UHLWI 0 33 en0
    10.1.1.15 0:30:18:ad:ed:ec UHLWI 0 269 en0 1125
    10.1.1.16 0:30:18:ad:ed:ec UHLWI 0 78 en0 1128
    10.1.1.21 0:c0:48:26:27:5e UHLWI 0 0 en0 1171
    10.1.1.21 0:c0:48:26:27:5e UHLWI 0 0 en1 1171
    10.1.1.100 127.0.0.1 UHS 0 0 lo0
    10.1.1.148 0:c:29:3e:40:c5 UHLWI 0 10 en0 1137
    10.1.1.157 127.0.0.1 UHS 0 1 lo0
    10.1.1.255 ff:ff:ff:ff:ff:ff UHLWbI 0 15 en0
    127 127.0.0.1 UCS 0 0 lo0
    127.0.0.1 127.0.0.1 UH 1 14 lo0

    Open Solaris 9
    ifconfig -a
    lo0: flags=2001000849<UP,LOOPBACK,RUNNING,MULTICAST,IPv 4,VIRTUAL> mtu 8232 index 1
    inet 127.0.0.1 netmask ff000000
    pcn0: flags=1004843<UP,BROADCAST,RUNNING,MULTICAST,DHCP, IPv4> mtu 1500 index 2
    inet 10.1.1.148 netmask ffffff00 broadcast 10.1.1.255
    pcn1: flags=1004843<UP,BROADCAST,RUNNING,MULTICAST,DHCP, IPv4> mtu 1500 index 3
    inet 10.1.1.125 netmask ffffff00 broadcast 10.1.1.255
    lo0: flags=2002000849<UP,LOOPBACK,RUNNING,MULTICAST,IPv 6,VIRTUAL> mtu 8252 index 1
    inet6 ::1/128

    Routing Table: IPv4
    Destination Gateway Flags Ref Use Interface
    -------------------- -------------------- ----- ----- ---------- ---------
    default 10.1.1.1 UG 1 2 pcn0
    default 10.1.1.1 UG 1 1 pcn1
    10.1.1.0 10.1.1.148 U 1 2 pcn0
    10.1.1.0 10.1.1.125 U 1 1 pcn1
    127.0.0.1 127.0.0.1 UH 1 28 lo0

    Routing Table: IPv6
    Destination/Mask Gateway Flags Ref Use If
    --------------------------- --------------------------- ----- --- ------- -----
    ::1 ::1 UH 1 0 lo0


    10.04
    eth0 Link encap:Ethernet HWaddr 00:0c:29:30:6f:8f
    inet addr:10.1.1.139 Bcast:10.1.1.255 Mask:255.255.255.0
    inet6 addr: fe80::20c:29ff:fe30:6f8f/64 Scope:Link
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:258 errors:0 dropped:0 overruns:0 frame:0
    TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000
    RX bytes:19342 (19.3 KB) TX bytes:1152 (1.1 KB)

    eth1 Link encap:Ethernet HWaddr 00:0c:29:30:6f:99
    inet addr:10.1.1.115 Bcast:10.1.1.255 Mask:255.255.255.0
    inet6 addr: fe80::20c:29ff:fe30:6f99/64 Scope:Link
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:1038 errors:0 dropped:0 overruns:0 frame:0
    TX packets:546 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000
    RX bytes:86839 (86.8 KB) TX bytes:157150 (157.1 KB)

    Kernel IP routing table
    Destination Gateway Genmask Flags Metric Ref Use Iface
    10.1.1.0 * 255.255.255.0 U 0 0 0 eth1
    10.1.1.0 * 255.255.255.0 U 0 0 0 eth0
    default blackbox.xxxx 0.0.0.0 UG 100 0 0 eth0
    default blackbox.xxxx 0.0.0.0 UG 100 0 0 eth1

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