Network loop control

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This topic contains 12 replies, has 4 voices, and was last updated by Avatar theterranaut 12 years, 8 months ago.

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    mariamislam
    Member
    #118124

    IF I have a server with 2 network cards, each connecting to different network. I have a router which defines and routes the trafic between these network. what are the chances of having a loop because of this server having 2 network cards?

    Avatar
    theterranaut
    Member
    #285846

    Re: Network loop control

    Its possible. You actually have 2 routers:

    -the ‘multihomed’ server (with 2 nic’s) is a router
    -so is the (I’m assuming) ‘hardware’ router

    You would really have to sit down and examine your topology- logical and physical- to see if a ‘loop’ is possible.

    Do you suspect there is one? Some strange behaviour?

    regards,

    theterranaut

    Avatar
    daviddavis
    Member
    #263677

    Re: Network loop control

    You could run a routing protocol on the server and the router. That way, they could communicate with each other and decide the best route, creating a “loop free” network.

    Although, for such a small network the trouble might not be worth the benefits. But that it up to you to decide.

    Thanks for your post!

    David

    JeremyW
    JeremyW
    Moderator
    #268199

    Re: Network loop control

    Wouldn’t RRAS have to be configured on the server to make a routing loop possible? Has the OP set the server up as a router? All the OP said was that he had a multihomed server…

    Just asking.

    Avatar
    theterranaut
    Member
    #285847

    Re: Network loop control

    hi Jeremy,
    yes, I see what you mean. But by default, unless you put packet filters
    on its interfaces, a W2K/2K3 server with a NIC in 2 separate networks
    will happily route between these networks. It seems to be something thats
    built into the OS. You can confirm this by shutting down a single NIC server,
    adding in another NIC, powering up, adding an IP on a different network
    for the new NIC, and issuing ‘route print’ at the command prompt. Hey presto,
    the routes appear! Just like connected routes in the Cisco world.

    Adding RRAS does add a lot more ‘functionality’, NAT’ing and such like, but
    the old “2 NICs, 1PC, 1 Copy of Windows Server 2003” makes a fairly functional
    (though restricted to Ethernet traffic) router.

    Cheers!

    theterranaut

    JeremyW
    JeremyW
    Moderator
    #268203

    Re: Network loop control

    Thanks TT. Is this functionality limited to the server OS? I did a little test and was unsuccessful.
    Here’s the configs:

    Computer1 OS=Win 2k Pro Subnet=172.18.21.0
    ===========================================================================
    Interface List
    0x1 ……………………… MS TCP Loopback interface
    0x1000003 …00 06 5b 90 48 34 …… 3Com EtherLink PCI
    ===========================================================================
    ===========================================================================
    Active Routes:
    Network Destination Netmask Gateway Interface Metric
    0.0.0.0 0.0.0.0 172.18.21.65 172.18.21.153 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    172.18.21.0 255.255.255.0 172.18.21.153 172.18.21.153 1
    172.18.21.153 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.18.255.255 255.255.255.255 172.18.21.153 172.18.21.153 1
    [B][COLOR=”Red”]172.19.12.0 255.255.255.0 172.18.21.130 172.18.21.153 1[/COLOR][/B]
    224.0.0.0 224.0.0.0 172.18.21.153 172.18.21.153 1
    255.255.255.255 255.255.255.255 172.18.21.153 172.18.21.153 1
    Default Gateway: 172.18.21.65
    ===========================================================================[/CODE]
    Computer2 (multihomed) OS=Win 2k Pro Subnet=both
    [CODE]===========================================================================
    Interface List
    0x1 ……………………… MS TCP Loopback interface
    0x1000003 …00 03 6d 00 83 92 …… Linksys LNE100TX Fast Ethernet Adapter (LN
    E100TX v4) NDIS5 Driver
    0x1000004 …00 06 5b dc 3b c6 …… 3Com EtherLink PCI
    ===========================================================================
    ===========================================================================
    Active Routes:
    Network Destination Netmask Gateway Interface Metric
    0.0.0.0 0.0.0.0 172.18.21.65 172.18.21.130 1
    0.0.0.0 0.0.0.0 172.19.12.129 172.19.12.62 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    172.18.21.0 255.255.255.0 172.18.21.130 172.18.21.130 1
    172.18.21.130 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.18.255.255 255.255.255.255 172.18.21.130 172.18.21.130 1
    172.19.12.0 255.255.255.0 172.19.12.62 172.19.12.62 1
    172.19.12.62 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.19.255.255 255.255.255.255 172.19.12.62 172.19.12.62 1
    224.0.0.0 224.0.0.0 172.18.21.130 172.18.21.130 1
    224.0.0.0 224.0.0.0 172.19.12.62 172.19.12.62 1
    255.255.255.255 255.255.255.255 172.18.21.130 172.18.21.130 1
    Default Gateway: 172.18.21.65
    ===========================================================================[/CODE]
    Computer3 OS=Win98se Subnet=172.19.12.0
    [CODE]Active Routes:

    Network Address Netmask Gateway Address Interface Metric
    0.0.0.0 0.0.0.0 172.19.12.129 172.19.12.145 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    [B][COLOR=”red”]172.18.21.0 255.255.255.0 172.19.12.62 172.19.12.145 1[/COLOR][/B]
    172.19.12.0 255.255.255.0 172.19.12.145 172.19.12.145 1
    172.19.12.145 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.19.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1
    224.0.0.0 224.0.0.0 172.19.12.145 172.19.12.145 1
    255.255.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1[/CODE]
    This KB alludes to the fact that you need to enable IP routing but the only place I’ve seen that setting is in RRAS. [url]http://support.microsoft.com/kb/140859[/url][CODE]===========================================================================
    Interface List
    0x1 ……………………… MS TCP Loopback interface
    0x1000003 …00 06 5b 90 48 34 …… 3Com EtherLink PCI
    ===========================================================================
    ===========================================================================
    Active Routes:
    Network Destination Netmask Gateway Interface Metric
    0.0.0.0 0.0.0.0 172.18.21.65 172.18.21.153 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    172.18.21.0 255.255.255.0 172.18.21.153 172.18.21.153 1
    172.18.21.153 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.18.255.255 255.255.255.255 172.18.21.153 172.18.21.153 1
    172.19.12.0 255.255.255.0 172.18.21.130 172.18.21.153 1
    224.0.0.0 224.0.0.0 172.18.21.153 172.18.21.153 1
    255.255.255.255 255.255.255.255 172.18.21.153 172.18.21.153 1
    Default Gateway: 172.18.21.65
    ===========================================================================[/CODE]
    Computer2 (multihomed) OS=Win 2k Pro Subnet=both
    ===========================================================================
    Interface List
    0x1 ……………………… MS TCP Loopback interface
    0x1000003 …00 03 6d 00 83 92 …… Linksys LNE100TX Fast Ethernet Adapter (LN
    E100TX v4) NDIS5 Driver
    0x1000004 …00 06 5b dc 3b c6 …… 3Com EtherLink PCI
    ===========================================================================
    ===========================================================================
    Active Routes:
    Network Destination Netmask Gateway Interface Metric
    0.0.0.0 0.0.0.0 172.18.21.65 172.18.21.130 1
    0.0.0.0 0.0.0.0 172.19.12.129 172.19.12.62 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    172.18.21.0 255.255.255.0 172.18.21.130 172.18.21.130 1
    172.18.21.130 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.18.255.255 255.255.255.255 172.18.21.130 172.18.21.130 1
    172.19.12.0 255.255.255.0 172.19.12.62 172.19.12.62 1
    172.19.12.62 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.19.255.255 255.255.255.255 172.19.12.62 172.19.12.62 1
    224.0.0.0 224.0.0.0 172.18.21.130 172.18.21.130 1
    224.0.0.0 224.0.0.0 172.19.12.62 172.19.12.62 1
    255.255.255.255 255.255.255.255 172.18.21.130 172.18.21.130 1
    Default Gateway: 172.18.21.65
    ===========================================================================[/CODE]
    Computer3 OS=Win98se Subnet=172.19.12.0
    [CODE]Active Routes:

    Network Address Netmask Gateway Address Interface Metric
    0.0.0.0 0.0.0.0 172.19.12.129 172.19.12.145 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    [B][COLOR=”red”]172.18.21.0 255.255.255.0 172.19.12.62 172.19.12.145 1[/COLOR][/B]
    172.19.12.0 255.255.255.0 172.19.12.145 172.19.12.145 1
    172.19.12.145 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.19.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1
    224.0.0.0 224.0.0.0 172.19.12.145 172.19.12.145 1
    255.255.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1[/CODE]
    This KB alludes to the fact that you need to enable IP routing but the only place I’ve seen that setting is in RRAS. [url]http://support.microsoft.com/kb/140859[/url][CODE]===========================================================================
    Interface List
    0x1 ……………………… MS TCP Loopback interface
    0x1000003 …00 03 6d 00 83 92 …… Linksys LNE100TX Fast Ethernet Adapter (LN
    E100TX v4) NDIS5 Driver
    0x1000004 …00 06 5b dc 3b c6 …… 3Com EtherLink PCI
    ===========================================================================
    ===========================================================================
    Active Routes:
    Network Destination Netmask Gateway Interface Metric
    0.0.0.0 0.0.0.0 172.18.21.65 172.18.21.130 1
    0.0.0.0 0.0.0.0 172.19.12.129 172.19.12.62 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    172.18.21.0 255.255.255.0 172.18.21.130 172.18.21.130 1
    172.18.21.130 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.18.255.255 255.255.255.255 172.18.21.130 172.18.21.130 1
    172.19.12.0 255.255.255.0 172.19.12.62 172.19.12.62 1
    172.19.12.62 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.19.255.255 255.255.255.255 172.19.12.62 172.19.12.62 1
    224.0.0.0 224.0.0.0 172.18.21.130 172.18.21.130 1
    224.0.0.0 224.0.0.0 172.19.12.62 172.19.12.62 1
    255.255.255.255 255.255.255.255 172.18.21.130 172.18.21.130 1
    Default Gateway: 172.18.21.65
    ===========================================================================[/CODE]
    Computer3 OS=Win98se Subnet=172.19.12.0
    Active Routes:

    Network Address Netmask Gateway Address Interface Metric
    0.0.0.0 0.0.0.0 172.19.12.129 172.19.12.145 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    [B][COLOR=”red”]172.18.21.0 255.255.255.0 172.19.12.62 172.19.12.145 1[/COLOR][/B]
    172.19.12.0 255.255.255.0 172.19.12.145 172.19.12.145 1
    172.19.12.145 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.19.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1
    224.0.0.0 224.0.0.0 172.19.12.145 172.19.12.145 1
    255.255.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1[/CODE]
    This KB alludes to the fact that you need to enable IP routing but the only place I’ve seen that setting is in RRAS. [url]http://support.microsoft.com/kb/140859[/url][CODE]Active Routes:

    Network Address Netmask Gateway Address Interface Metric
    0.0.0.0 0.0.0.0 172.19.12.129 172.19.12.145 1
    127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
    172.18.21.0 255.255.255.0 172.19.12.62 172.19.12.145 1
    172.19.12.0 255.255.255.0 172.19.12.145 172.19.12.145 1
    172.19.12.145 255.255.255.255 127.0.0.1 127.0.0.1 1
    172.19.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1
    224.0.0.0 224.0.0.0 172.19.12.145 172.19.12.145 1
    255.255.255.255 255.255.255.255 172.19.12.145 172.19.12.145 1[/CODE]
    This KB alludes to the fact that you need to enable IP routing but the only place I’ve seen that setting is in RRAS. http://support.microsoft.com/kb/140859

    Avatar
    theterranaut
    Member
    #285848

    Re: Network loop control

    Thanks Jeremy,

    I’m away from the lab just now and cant check that I actually had to do anything additional… damn, you’ve got me thinking now!

    I do remember it being incredibly sensitive to daft things like the order in which the nics get assigned IP’s and whether or not the respective interfaces had gateways or not. It basically creates the routes as the IPs get setup. I now distinctly remember having to play with the gateways and ridding myself of one of the default routes..I’ll have to get back to you on this!

    Actually, can you check those gateways on the workstations for me:

    Computer#1: (172.18.21.0 network side) has an interface of 172.18.21.153, gateway of .65
    Computer#3: (172.19.12.0 network side) has an interface of .145, gateway of 172.19.12.129 yes?

    But looking at the multihomed box, I see:
    Interface: 172.18.21.130
    Interface: 172.19.12.62

    As I say, I’m riffing a bit here and may be misreading this (got roped into helping out with some imaging tonight ) but I think you’ll find that the gateways of 1 and 3 need to correspond to the nics on either side of the multihomed machine, ie, .130 and .62.

    (I’m gently preparing myself for the embarrassment of seeing that I have, in fact, stuck RRAS on that box after all…)

    :confused:

    theterranaut

    JeremyW
    JeremyW
    Moderator
    #268208

    Re: Network loop control

    I’ll give changing the gateways a shot but you’ll notice I did configure static routes to the respective subnets. (Bolded above and now I’ll make them red as well)

    JeremyW
    JeremyW
    Moderator
    #268209

    Re: Network loop control

    I changed the default gateway on both the Win 2k and 98se to 172.18.21.130 and 172.19.12.62 respectively. Still nothing (echo requests) was routed to the other subnet.

    Let me know what you find TT.

    Thanks.

    EDIT – :oops: just read “I now distinctly remember having to play with the gateways and ridding myself of one of the default routes”. I missed that before. I’ll try that and see what happens.

    Avatar
    mariamislam
    Member
    #225361

    Re: Network loop control

    Guys,
    Thank you very much for your input. I am novice in this field, so I am trying my best to have my network stable.

    I would apprciate if you can provide me links to tools for network monitoring, so that I can identify where problems are so that I can be proactive in my network administration activities.

    I also would like to know what settings are critical to be enable in every switch in a network?

    Thanking you.

    JeremyW
    JeremyW
    Moderator
    #268226

    Re: Network loop control

    mariamislam;47206 wrote:
    I would apprciate if you can provide me links to tools for network monitoring, so that I can identify where problems are so that I can be proactive in my network administration activities.

    Check out Wireshark http://www.wireshark.org/

    Quote:
    I also would like to know what settings are critical to be enable in every switch in a network?

    Others would be able to give you advice on this.

    TT, I had a few extra minutes and I took one of the gateways out on the multihomed computer. Here’s what happened:

    Computer1 = 172.18.21.153 gateway 172.18.21.130
    Computer2 = 172.18.21.130 gateway 172.18.21.65 (IF 1)
    Computer2 = 172.19.12.146 gateway none (IF 2)
    Computer3 = 172.19.12.145 gateway 172.19.12.146

    Computer1
    -ping 172.18.21.130 successful
    -ping 172.19.12.146 successful
    -ping 172.19.12.145 unsuccessful

    Computer2
    -ping 172.18.21.153 successful
    -ping 172.19.12.145 successful

    Computer3
    -ping 172.19.12.146 successful
    -ping 172.18.21.130 successful
    -ping 172.18.21.153 unsuccessful

    Avatar
    theterranaut
    Member
    #285849

    Re: Network loop control

    Hi Jeremy,
    sorry I’ve not been back to get into this, I’ve been away from my lab for a few days o cant really test/check configs.

    Thats interesting- it looks as though its not being returned from the respective gateway on the other side. I ‘ll get back onto this one as soon as I can.

    Sorry guys-

    theterranaut

    JeremyW
    JeremyW
    Moderator
    #268260

    Re: Network loop control

    theterranaut;47780 wrote:
    Hi Jeremy,
    sorry I’ve not been back to get into this, I’ve been away from my lab for a few days o cant really test/check configs.

    Thats interesting- it looks as though its not being returned from the respective gateway on the other side. I ‘ll get back onto this one as soon as I can.

    Sorry guys-

    theterranaut

    Hey no obligations here. Take your time. :)

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