CEF & static routes

Discussion in 'Cisco' started by Sami, Oct 6, 2004.

  1. Sami

    Sami Guest

    Hi,

    I have a problem with static routes:

    I have a Cisco 3750 which is connected to 3rd party router via 2 100Mbit/s
    FastEthernet ports.

    The interfaces in the 3rd party router towards 3750 are X.X.X.X and Y.Y.Y.Y.
    There is a route called Z.Z.Z.Z/24 behind this 3rd party router. I have
    configured 2 static routes into 3750 which are:

    IP ROUTE Z.Z.Z.Z 255.255.255.0 X.X.X.X
    IP ROUTE Z.Z.Z.Z 255.255.255.0 Y.Y.Y.Y

    now everything works well if both interfaces between 3750 and the 3rd party
    router are up but if I put one of the interfaces down with the SHUTDOWN
    command, the ping to the Z.Z.Z.Z looks like this:

    !.!.!.!

    Why does this happen? Does it have something to do with the CEF?

    -Sami R
     
    Sami, Oct 6, 2004
    #1
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  2. Sami

    Ivan Ostreš Guest

    In article <psL8d.27067$>,
    says...
    > Subject: CEF & static routes
    > From: "Sami" <>
    > Organization: Nokia
    > Newsgroups: comp.dcom.sys.cisco
    >
    > Hi,
    >
    > I have a problem with static routes:
    >
    > I have a Cisco 3750 which is connected to 3rd party router via 2 100Mbit/s
    > FastEthernet ports.
    >
    > The interfaces in the 3rd party router towards 3750 are X.X.X.X and Y.Y.Y.Y.
    > There is a route called Z.Z.Z.Z/24 behind this 3rd party router. I have
    > configured 2 static routes into 3750 which are:
    >
    > IP ROUTE Z.Z.Z.Z 255.255.255.0 X.X.X.X
    > IP ROUTE Z.Z.Z.Z 255.255.255.0 Y.Y.Y.Y
    >
    > now everything works well if both interfaces between 3750 and the 3rd party
    > router are up but if I put one of the interfaces down with the SHUTDOWN
    > command, the ping to the Z.Z.Z.Z looks like this:
    >
    > !.!.!.!
    >
    > Why does this happen? Does it have something to do with the CEF?
    >
    >


    The thing is that router originated packets are process switched, not
    CEF switched.

    Do you loose one of the routes from routing table when you do shutdown
    of the interface? Does the 3rd party router looses the same route?

    I would try traceroute from both routers few times, it might give you a
    clue.

    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Oct 6, 2004
    #2
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  3. Sami

    AnyBody43 Guest

    "Sami" <> wrote
    > I have a problem with static routes:
    >
    > I have a Cisco 3750 which is connected to 3rd party router via 2 100Mbit/s
    > FastEthernet ports.
    >
    > The interfaces in the 3rd party router towards 3750 are X.X.X.X and Y.Y.Y.Y.
    > There is a route called Z.Z.Z.Z/24 behind this 3rd party router. I have
    > configured 2 static routes into 3750 which are:
    >
    > IP ROUTE Z.Z.Z.Z 255.255.255.0 X.X.X.X
    > IP ROUTE Z.Z.Z.Z 255.255.255.0 Y.Y.Y.Y
    >
    > now everything works well if both interfaces between 3750 and the 3rd party
    > router are up but if I put one of the interfaces down with the SHUTDOWN
    > command, the ping to the Z.Z.Z.Z looks like this:
    >
    > !.!.!.!


    This will happen if you have Vlan interfaces defined on the 3750
    and the physical interfaces are Layer 2 only and you are using per
    packet load sharing.

    You may be able to solve this particular problem by configuring the
    physical interfaces as Layer 3 interfaces with IP addresses. This
    "solution" however may only move the problem one hop out.

    The latest greatest IOS releases provides "Policy Based Routing
    with the Multiple Tracking Options"
    http://www.cisco.com/en/US/tech/tk364/tk871/technologies_configuration_example09186a0080211f5c.shtml

    "The Multiple Tracking Options feature is most suitable for routers
    which have multiple Ethernet connections as the next hop."

    It is however brand new and may not be available on the 3750, sorry
    look yourself.

    Consider:-
    hsrp (or vrrp), dynamic routing,
    as simpler, tried and tested solutions. These may require a minor or
    major re-design.
     
    AnyBody43, Oct 6, 2004
    #3
  4. Sami

    Sami Guest

    "AnyBody43" <> wrote in message
    news:...
    > "Sami" <> wrote
    >> I have a problem with static routes:
    >>
    >> I have a Cisco 3750 which is connected to 3rd party router via 2
    >> 100Mbit/s
    >> FastEthernet ports.
    >>
    >> The interfaces in the 3rd party router towards 3750 are X.X.X.X and
    >> Y.Y.Y.Y.
    >> There is a route called Z.Z.Z.Z/24 behind this 3rd party router. I have
    >> configured 2 static routes into 3750 which are:
    >>
    >> IP ROUTE Z.Z.Z.Z 255.255.255.0 X.X.X.X
    >> IP ROUTE Z.Z.Z.Z 255.255.255.0 Y.Y.Y.Y
    >>
    >> now everything works well if both interfaces between 3750 and the 3rd
    >> party
    >> router are up but if I put one of the interfaces down with the SHUTDOWN
    >> command, the ping to the Z.Z.Z.Z looks like this:
    >>
    >> !.!.!.!

    >
    > This will happen if you have Vlan interfaces defined on the 3750
    > and the physical interfaces are Layer 2 only and you are using per
    > packet load sharing.
    >
    > You may be able to solve this particular problem by configuring the
    > physical interfaces as Layer 3 interfaces with IP addresses. This
    > "solution" however may only move the problem one hop out.
    >
    > The latest greatest IOS releases provides "Policy Based Routing
    > with the Multiple Tracking Options"
    > http://www.cisco.com/en/US/tech/tk364/tk871/technologies_configuration_example09186a0080211f5c.shtml
    >
    > "The Multiple Tracking Options feature is most suitable for routers
    > which have multiple Ethernet connections as the next hop."
    >
    > It is however brand new and may not be available on the 3750, sorry
    > look yourself.
    >
    > Consider:-
    > hsrp (or vrrp), dynamic routing,
    > as simpler, tried and tested solutions. These may require a minor or
    > major re-design.


    You are right...There is a VLAN trunk defined, in fact I have two 3750
    interconnected via portchannel and there is a HSRP group defined for
    both VLANs (Those ports to the 3rd party router are in separate VLANs)
    and the ports are L2 ports as you mentioned...

    I changed the ports to L3 ports and made a HSRP group under these ports
    and now it works but the VLAN feature is lost...I'll have to check that
    Cisco's new software out...

    Many thanks to everyone !

    -Sami
     
    Sami, Oct 6, 2004
    #4
  5. Sami

    Hansang Bae Guest

    In article <psL8d.27067$>,
    says...
    > Hi,
    >
    > I have a problem with static routes:
    >
    > I have a Cisco 3750 which is connected to 3rd party router via 2 100Mbit/s
    > FastEthernet ports.
    >
    > The interfaces in the 3rd party router towards 3750 are X.X.X.X and Y.Y.Y.Y.
    > There is a route called Z.Z.Z.Z/24 behind this 3rd party router. I have
    > configured 2 static routes into 3750 which are:
    >
    > IP ROUTE Z.Z.Z.Z 255.255.255.0 X.X.X.X
    > IP ROUTE Z.Z.Z.Z 255.255.255.0 Y.Y.Y.Y
    >
    > now everything works well if both interfaces between 3750 and the 3rd party
    > router are up but if I put one of the interfaces down with the SHUTDOWN
    > command, the ping to the Z.Z.Z.Z looks like this:
    >
    > !.!.!.!
    >
    > Why does this happen? Does it have something to do with the CEF?


    Are there other ports in the vlan to keep the L3 information up?
    Besides, you should be using routing and not statics.


    --

    hsb

    "Somehow I imagined this experience would be more rewarding" Calvin
    *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
    ********************************************************************
    Due to the volume of email that I receive, I may not not be able to
    reply to emails sent to my account. Please post a followup instead.
    ********************************************************************
     
    Hansang Bae, Oct 6, 2004
    #5
  6. Sami

    Sami Guest

    "Hansang Bae" <> wrote in message
    news:...
    > In article <psL8d.27067$>,
    > says...
    > > Hi,
    > >
    > > I have a problem with static routes:
    > >
    > > I have a Cisco 3750 which is connected to 3rd party router via 2

    100Mbit/s
    > > FastEthernet ports.
    > >
    > > The interfaces in the 3rd party router towards 3750 are X.X.X.X and

    Y.Y.Y.Y.
    > > There is a route called Z.Z.Z.Z/24 behind this 3rd party router. I have
    > > configured 2 static routes into 3750 which are:
    > >
    > > IP ROUTE Z.Z.Z.Z 255.255.255.0 X.X.X.X
    > > IP ROUTE Z.Z.Z.Z 255.255.255.0 Y.Y.Y.Y
    > >
    > > now everything works well if both interfaces between 3750 and the 3rd

    party
    > > router are up but if I put one of the interfaces down with the SHUTDOWN
    > > command, the ping to the Z.Z.Z.Z looks like this:
    > >
    > > !.!.!.!
    > >
    > > Why does this happen? Does it have something to do with the CEF?

    >
    > Are there other ports in the vlan to keep the L3 information up?
    > Besides, you should be using routing and not statics.
    >



    The 3rd party router is a very special equipment and it does not support any
    routing
    protocols so we must use static routes and we are also instructed to use
    different VLANs in
    both interfaces. The basic idea is to have a redundant link between these
    routers and use
    the per destination load balancing due to voice traffic between these
    routers...

    If you have any idea how to implement this kind of link...I'm listening...

    -Sami

    >
    > --
    >
    > hsb
    >
    > "Somehow I imagined this experience would be more rewarding" Calvin
    > *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
    > ********************************************************************
    > Due to the volume of email that I receive, I may not not be able to
    > reply to emails sent to my account. Please post a followup instead.
    > ********************************************************************
     
    Sami, Oct 7, 2004
    #6
  7. Sami

    Sami Guest

    "Hansang Bae" <> wrote in message
    news:...
    > In article <psL8d.27067$>,
    > says...
    > > Hi,
    > >
    > > I have a problem with static routes:
    > >
    > > I have a Cisco 3750 which is connected to 3rd party router via 2

    100Mbit/s
    > > FastEthernet ports.
    > >
    > > The interfaces in the 3rd party router towards 3750 are X.X.X.X and

    Y.Y.Y.Y.
    > > There is a route called Z.Z.Z.Z/24 behind this 3rd party router. I have
    > > configured 2 static routes into 3750 which are:
    > >
    > > IP ROUTE Z.Z.Z.Z 255.255.255.0 X.X.X.X
    > > IP ROUTE Z.Z.Z.Z 255.255.255.0 Y.Y.Y.Y
    > >
    > > now everything works well if both interfaces between 3750 and the 3rd

    party
    > > router are up but if I put one of the interfaces down with the SHUTDOWN
    > > command, the ping to the Z.Z.Z.Z looks like this:
    > >
    > > !.!.!.!
    > >
    > > Why does this happen? Does it have something to do with the CEF?

    >
    > Are there other ports in the vlan to keep the L3 information up?
    > Besides, you should be using routing and not statics.


    In fact there is...we have two 3750 connected together via etherchannel and
    they are using HSRP groups for every VLAN...there are these 3rd party
    routers connected
    to both 3750's but they are not used at the same time...if one of these 3rd
    routers goes down, there is an automatic switchover to the other.

    To have even more resiliency beside this switchover, both 3rd routers are
    connected
    with two links to the 3750 routers. When operating normally, per destination
    load balancing is done
    with these two links...but if one of the two links goes down an automatic
    switchover happens and the other 3rd router passes the traffic...but if
    there is a case
    where after this switcover one of the two links to this router goes down we
    want
    the traffic to move to the other link.

    -Sami

    >
    >
    > --
    >
    > hsb
    >
    > "Somehow I imagined this experience would be more rewarding" Calvin
    > *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
    > ********************************************************************
    > Due to the volume of email that I receive, I may not not be able to
    > reply to emails sent to my account. Please post a followup instead.
    > ********************************************************************
     
    Sami, Oct 7, 2004
    #7
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