routing problem

Discussion in 'Cisco' started by Sebastien Mazeau, Apr 5, 2004.

  1. Hello,

    As the title says, I have a (static) routing problem; please consider the
    small network below:

    LAN1 --- E0 /Cisco R1/ S1 --- MPLS Network --- S0 /Cisco R2/ E0 ----
    LAN2 --- E0 /Non-Cisco R3/ E1 --- LAN3

    LAN1: 192.168.1.0/24
    LAN2: 192.168.11.0/24
    LAN3: 192.168.30.0/24

    R1
    E0: 192.168.1.11
    S1: 192.168.171.2/30

    R1 Routing table:
    192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    C 192.168.171.1/32 is directly connected, Serial1
    C 192.168.171.0/30 is directly connected, Serial1
    C 192.168.1.0/24 is directly connected, Ethernet0
    S* 0.0.0.0/0 [1/0] via 192.168.1.13
    S 192.168.0.0/16 [1/0] via 192.168.171.1
    S 192.168.30.0/24 [1/0] via 192.168.11.11

    R2
    E0: 192.168.11.11
    S0: 192.168.171.18/30

    R2 Routing table:
    C 192.168.11.0/24 is directly connected, Ethernet0
    192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    C 192.168.171.17/32 is directly connected, Serial0
    C 192.168.171.16/30 is directly connected, Serial0
    S 192.168.1.0/24 [1/0] via 192.168.171.17
    S* 0.0.0.0/0 [1/0] via 192.168.11.14
    S 192.168.1.0/24 [1/0] via 192.168.171.17
    S 192.168.30.0/24 [1/0] via 192.168.11.14

    R3
    E0: 192.168.11.14

    There is no access-list set anywhere on R1, R2 or R3.
    I do not control the MPLS network..
    Please do not care about R3, and consider that it is set correctly (for the
    routing part anyway).

    Problem:
    Pings to 192.168.30.0/24 from 192.168.1.0/24 have no answer. What should I
    do so that pings have a reply ?

    A trace performed on R1 (source: 192.168.1.11 destination: 192.168.30.101)
    gives me this:

    1 192.168.171.1 116 msec 28 msec 28 msec
    2 192.168.171.2 28 msec 92 msec 104 msec
    3 192.168.171.1 212 msec 60 msec 212 msec
    4 192.168.171.2 228 msec 68 msec 232 msec
    5 192.168.171.1 244 msec 116 msec 312 msec
    6 192.168.171.2 264 msec 320 msec 316 msec
    7 192.168.171.1 248 msec 1040 msec 156 msec
    8 192.168.171.2 476 msec 324 msec 432 msec
    9 192.168.171.1 320 msec 376 msec 436 msec
    10 192.168.171.2 644 msec 240 msec 736 msec

    A loop ! And pings do not reach even R2

    Any one has an idea ? Any remarks welcome.

    Thanks in advance,

    Sebastien
    Sebastien Mazeau, Apr 5, 2004
    #1
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  2. In article <407104bb$0$19468$>,
    Sebastien Mazeau <> wrote:

    [snip]

    >LAN1 --- E0 /Cisco R1/ S1 --- MPLS Network --- S0 /Cisco R2/ E0 ----
    >LAN2 --- E0 /Non-Cisco R3/ E1 --- LAN3
    >
    >LAN1: 192.168.1.0/24
    >LAN2: 192.168.11.0/24
    >LAN3: 192.168.30.0/24
    >
    >R1
    >E0: 192.168.1.11
    >S1: 192.168.171.2/30
    >
    >R1 Routing table:
    > 192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    >C 192.168.171.1/32 is directly connected, Serial1
    >C 192.168.171.0/30 is directly connected, Serial1
    >C 192.168.1.0/24 is directly connected, Ethernet0
    >S* 0.0.0.0/0 [1/0] via 192.168.1.13
    >S 192.168.0.0/16 [1/0] via 192.168.171.1
    >S 192.168.30.0/24 [1/0] via 192.168.11.11
    >
    >R2
    >E0: 192.168.11.11
    >S0: 192.168.171.18/30
    >
    >R2 Routing table:
    >C 192.168.11.0/24 is directly connected, Ethernet0
    > 192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    >C 192.168.171.17/32 is directly connected, Serial0
    >C 192.168.171.16/30 is directly connected, Serial0
    >S 192.168.1.0/24 [1/0] via 192.168.171.17
    >S* 0.0.0.0/0 [1/0] via 192.168.11.14
    >S 192.168.1.0/24 [1/0] via 192.168.171.17
    >S 192.168.30.0/24 [1/0] via 192.168.11.14
    >
    >R3
    >E0: 192.168.11.14
    >
    >There is no access-list set anywhere on R1, R2 or R3.
    >I do not control the MPLS network..
    >Please do not care about R3, and consider that it is set correctly (for the
    >routing part anyway).
    >
    >Problem:
    >Pings to 192.168.30.0/24 from 192.168.1.0/24 have no answer. What should I
    >do so that pings have a reply ?


    [snip]

    >A loop ! And pings do not reach even R2
    >
    >Any one has an idea ? Any remarks welcome.


    It's desirable to set up a single /30 subnet for both sides of a
    serial connection - so R1 and R2 should have just one /30 assigned
    between them - ie use the 192.168.172.2/30 network for R1/S1 and
    192.168.172.1/30 for R2/S0 - that way there is only one identifier for
    those interfaces - it reduces future confusion and enables pinging
    between the two routers.

    Secondly - I know you said to assume that R3 is configured properly,
    but make sure it has a a default route (and ip-subnet zero turned on
    if it's a Cisco running an IOS that doesn't set that by default)
    pointing at R2 and/or have a route for 192.168.1.0/24 pointing at R2
    so that it knows to send packets for that network back to R2.

    Since R1 and R2 don't share a common subnet, they end up routing
    packets back and forth aimed at a destination that neither knows how
    to deliver locally, causing loops...

    Darin
    www.deru.net
    Darin Wayrynen, Apr 5, 2004
    #2
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  3. "Darin Wayrynen" <> wrote in message
    news:duacc.12372690$...
    > In article <407104bb$0$19468$>,
    > Sebastien Mazeau <> wrote:
    >
    > [snip]
    >
    > >LAN1 --- E0 /Cisco R1/ S1 --- MPLS Network --- S0 /Cisco R2/ E0 ----
    > >LAN2 --- E0 /Non-Cisco R3/ E1 --- LAN3
    > >
    > >LAN1: 192.168.1.0/24
    > >LAN2: 192.168.11.0/24
    > >LAN3: 192.168.30.0/24
    > >
    > >R1
    > >E0: 192.168.1.11
    > >S1: 192.168.171.2/30
    > >
    > >R1 Routing table:
    > > 192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    > >C 192.168.171.1/32 is directly connected, Serial1
    > >C 192.168.171.0/30 is directly connected, Serial1
    > >C 192.168.1.0/24 is directly connected, Ethernet0
    > >S* 0.0.0.0/0 [1/0] via 192.168.1.13
    > >S 192.168.0.0/16 [1/0] via 192.168.171.1
    > >S 192.168.30.0/24 [1/0] via 192.168.11.11
    > >
    > >R2
    > >E0: 192.168.11.11
    > >S0: 192.168.171.18/30
    > >
    > >R2 Routing table:
    > >C 192.168.11.0/24 is directly connected, Ethernet0
    > > 192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    > >C 192.168.171.17/32 is directly connected, Serial0
    > >C 192.168.171.16/30 is directly connected, Serial0
    > >S 192.168.1.0/24 [1/0] via 192.168.171.17
    > >S* 0.0.0.0/0 [1/0] via 192.168.11.14
    > >S 192.168.1.0/24 [1/0] via 192.168.171.17
    > >S 192.168.30.0/24 [1/0] via 192.168.11.14
    > >
    > >R3
    > >E0: 192.168.11.14
    > >
    > >There is no access-list set anywhere on R1, R2 or R3.
    > >I do not control the MPLS network..
    > >Please do not care about R3, and consider that it is set correctly (for

    the
    > >routing part anyway).
    > >
    > >Problem:
    > >Pings to 192.168.30.0/24 from 192.168.1.0/24 have no answer. What should

    I
    > >do so that pings have a reply ?

    >
    > [snip]
    >
    > >A loop ! And pings do not reach even R2
    > >


    >
    > It's desirable to set up a single /30 subnet for both sides of a
    > serial connection - so R1 and R2 should have just one /30 assigned
    > between them - ie use the 192.168.172.2/30 network for R1/S1 and
    > 192.168.172.1/30 for R2/S0 - that way there is only one identifier for
    > those interfaces - it reduces future confusion and enables pinging
    > between the two routers.


    The default gateway on R1/S1 is 192.168.171.1/30, and the default gateway on
    R2/S2 is 192.168.171.17/30.
    So the loop I saw was R1 sending a packet to its gateway which returned it
    back to R1 .
    I think these gateways are PE equipment, right (R1 and R2 are CPE) ? Can we
    imagine that the service provider tries to do all the routing in its
    equipment, and as of course he has never heard of LAN3 (because I didn't
    tell him, and I don't want to), he doesn't know where to route ?

    I may be saying something stupid or plenty obvious, but I don't know MPLS,
    so....

    [cut]

    > Since R1 and R2 don't share a common subnet, they end up routing
    > packets back and forth aimed at a destination that neither knows how
    > to deliver locally, causing loops...


    But I can ping LAN2 from LAN1; R1 has no route to LAN2 on its routing table,
    it has a route to 192.168.0.0/16 via its serial interface's gateway, and it
    can find its path to LAN2 ! One thing I didn't say: our network is a
    hub-and-spoke topology, and the hub is precisely R1, eg there are LAN4, LAN5
    ..... LAN8, all linked to R1 (ping has a reply both ways), although the only
    route in R1 to these LANs is 192.168.0.0/16. So the more I think to it, the
    more I believe that the routing is actually done on these gateways,
    controlled by the service provider. And if I add a new subnet somewhere, I
    can't solve this problem by just adding entries in the routing tables of MY
    routers.

    Does this make sense ?

    Sebastien
    Sebastien Mazeau, Apr 5, 2004
    #3
  4. Hi,

    In case someone is interested in the answer...

    My feeling was right, as the PE equipment have never heard of LAN3, it can
    not route the traffic from LAN1 to LAN3; equipment of the carrier is the
    cause of my problem. For this to work, I should ask the carrier to change
    its equipment's routing table (I won't ask, because it costs money).

    Now I have to find a solution to by-pass their PE equipment's routing. If
    anyone has an idea, thank you to let me know (though I've got some ideas I
    have to test).

    Sebastien


    "Sebastien Mazeau" <> wrote in message
    news:4071830b$0$14406$...
    >
    > "Darin Wayrynen" <> wrote in message
    > news:duacc.12372690$...
    > > In article <407104bb$0$19468$>,
    > > Sebastien Mazeau <> wrote:
    > >
    > > [snip]
    > >
    > > >LAN1 --- E0 /Cisco R1/ S1 --- MPLS Network --- S0 /Cisco R2/ E0 ----
    > > >LAN2 --- E0 /Non-Cisco R3/ E1 --- LAN3
    > > >
    > > >LAN1: 192.168.1.0/24
    > > >LAN2: 192.168.11.0/24
    > > >LAN3: 192.168.30.0/24
    > > >
    > > >R1
    > > >E0: 192.168.1.11
    > > >S1: 192.168.171.2/30
    > > >
    > > >R1 Routing table:
    > > > 192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    > > >C 192.168.171.1/32 is directly connected, Serial1
    > > >C 192.168.171.0/30 is directly connected, Serial1
    > > >C 192.168.1.0/24 is directly connected, Ethernet0
    > > >S* 0.0.0.0/0 [1/0] via 192.168.1.13
    > > >S 192.168.0.0/16 [1/0] via 192.168.171.1
    > > >S 192.168.30.0/24 [1/0] via 192.168.11.11
    > > >
    > > >R2
    > > >E0: 192.168.11.11
    > > >S0: 192.168.171.18/30
    > > >
    > > >R2 Routing table:
    > > >C 192.168.11.0/24 is directly connected, Ethernet0
    > > > 192.168.171.0/24 is variably subnetted, 2 subnets, 2 masks
    > > >C 192.168.171.17/32 is directly connected, Serial0
    > > >C 192.168.171.16/30 is directly connected, Serial0
    > > >S 192.168.1.0/24 [1/0] via 192.168.171.17
    > > >S* 0.0.0.0/0 [1/0] via 192.168.11.14
    > > >S 192.168.1.0/24 [1/0] via 192.168.171.17
    > > >S 192.168.30.0/24 [1/0] via 192.168.11.14
    > > >
    > > >R3
    > > >E0: 192.168.11.14
    > > >
    > > >There is no access-list set anywhere on R1, R2 or R3.
    > > >I do not control the MPLS network..
    > > >Please do not care about R3, and consider that it is set correctly (for

    > the
    > > >routing part anyway).
    > > >
    > > >Problem:
    > > >Pings to 192.168.30.0/24 from 192.168.1.0/24 have no answer. What

    should
    > I
    > > >do so that pings have a reply ?

    > >
    > > [snip]
    > >
    > > >A loop ! And pings do not reach even R2
    > > >

    >
    > >
    > > It's desirable to set up a single /30 subnet for both sides of a
    > > serial connection - so R1 and R2 should have just one /30 assigned
    > > between them - ie use the 192.168.172.2/30 network for R1/S1 and
    > > 192.168.172.1/30 for R2/S0 - that way there is only one identifier for
    > > those interfaces - it reduces future confusion and enables pinging
    > > between the two routers.

    >
    > The default gateway on R1/S1 is 192.168.171.1/30, and the default gateway

    on
    > R2/S2 is 192.168.171.17/30.
    > So the loop I saw was R1 sending a packet to its gateway which returned it
    > back to R1 .
    > I think these gateways are PE equipment, right (R1 and R2 are CPE) ? Can

    we
    > imagine that the service provider tries to do all the routing in its
    > equipment, and as of course he has never heard of LAN3 (because I didn't
    > tell him, and I don't want to), he doesn't know where to route ?
    >
    > I may be saying something stupid or plenty obvious, but I don't know MPLS,
    > so....
    >
    > [cut]
    >
    > > Since R1 and R2 don't share a common subnet, they end up routing
    > > packets back and forth aimed at a destination that neither knows how
    > > to deliver locally, causing loops...

    >
    > But I can ping LAN2 from LAN1; R1 has no route to LAN2 on its routing

    table,
    > it has a route to 192.168.0.0/16 via its serial interface's gateway, and

    it
    > can find its path to LAN2 ! One thing I didn't say: our network is a
    > hub-and-spoke topology, and the hub is precisely R1, eg there are LAN4,

    LAN5
    > .... LAN8, all linked to R1 (ping has a reply both ways), although the

    only
    > route in R1 to these LANs is 192.168.0.0/16. So the more I think to it,

    the
    > more I believe that the routing is actually done on these gateways,
    > controlled by the service provider. And if I add a new subnet somewhere, I
    > can't solve this problem by just adding entries in the routing tables of

    MY
    > routers.
    >
    > Does this make sense ?
    >
    > Sebastien
    >
    >
    Sebastien Mazeau, Apr 9, 2004
    #4
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