load balancing with a failover

Discussion in 'Cisco' started by yo, Mar 3, 2006.

  1. yo

    yo Guest

    ok, im not sure if this is possible but if it is im sure someone here
    knows how to get this working.


    i have a router with 3 t1 links. im doing per packet load balancing on
    the 1st 2 with the 3rd one being in admin down state and i only bring
    it up when they need additional bandwidth.

    i want to conver this 3rd line into a fail over link, so that when one
    of the 2 active load balancing lines goes down, the 3rd line will do
    load balancing with the line that did not go down.

    is this possible and how can i go about it. fyi im using eigrp routing
    and per packet loading.


    Thanks P
    yo, Mar 3, 2006
    #1
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  2. "backup interface" and dialer dtr should do it. Dialer DTR may or
    may not be an option, depending on your physical hardware. If you
    don't have it, then you may have to use something exotic like
    IP SLAs.

    Here I assume that you mean for the backup link truly to go up or
    down automatically according to your policy. If all you are concerned
    about is the path your IP forwarding should take (and you don't REALLY
    need to bring links up/down at a lower layer), then is a simple job
    for EIGRP metrics or floating statics or whatever floats your boat.

    Aaron

    ---

    ~ ok, im not sure if this is possible but if it is im sure someone here
    ~ knows how to get this working.
    ~
    ~
    ~ i have a router with 3 t1 links. im doing per packet load balancing on
    ~ the 1st 2 with the 3rd one being in admin down state and i only bring
    ~ it up when they need additional bandwidth.
    ~
    ~ i want to conver this 3rd line into a fail over link, so that when one
    ~ of the 2 active load balancing lines goes down, the 3rd line will do
    ~ load balancing with the line that did not go down.
    ~
    ~ is this possible and how can i go about it. fyi im using eigrp routing
    ~ and per packet loading.
    ~
    ~
    ~ Thanks P
    Aaron Leonard, Mar 3, 2006
    #2
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  3. yo

    Charlie Root Guest

    <yo> wrote in message news:...
    > ok, im not sure if this is possible but if it is im sure someone here
    > knows how to get this working.
    >
    >
    > i have a router with 3 t1 links. im doing per packet load balancing on
    > the 1st 2 with the 3rd one being in admin down state and i only bring
    > it up when they need additional bandwidth.
    >
    > i want to conver this 3rd line into a fail over link, so that when one
    > of the 2 active load balancing lines goes down, the 3rd line will do
    > load balancing with the line that did not go down.
    >


    you could use 'backup interface <name_of_backup_interface>' command in
    primary interface configuration. Here is what happens:

    CE-2.LAB(config)#in se 0/0:0
    CE-2.LAB(config-if)#backup interface atm0/1
    *Sep 6 13:24:43.174: %LINK-5-CHANGED: Interface ATM0/1, changed state to
    standby mode

    Unfortunately this is 1:1 redundancy, i.e. you can't specify the same backup
    interface for two primary interfaces. However, if all of your three lines
    are of the same bandwidth and connected to the same routers, why don't you
    just bundle them into multi-link PPP or do per-packet load-balancing across
    all three lines?

    Kind regards,
    iLya
    Charlie Root, Mar 3, 2006
    #3
  4. yo

    yo Guest

    its a cost thing they dont want to load balance the 3rd line and only
    want it as a backup solution.



    On Fri, 3 Mar 2006 22:09:17 +0100, "Charlie Root"
    <> wrote:

    ><yo> wrote in message news:...
    >> ok, im not sure if this is possible but if it is im sure someone here
    >> knows how to get this working.
    >>
    >>
    >> i have a router with 3 t1 links. im doing per packet load balancing on
    >> the 1st 2 with the 3rd one being in admin down state and i only bring
    >> it up when they need additional bandwidth.
    >>
    >> i want to conver this 3rd line into a fail over link, so that when one
    >> of the 2 active load balancing lines goes down, the 3rd line will do
    >> load balancing with the line that did not go down.
    >>

    >
    >you could use 'backup interface <name_of_backup_interface>' command in
    >primary interface configuration. Here is what happens:
    >
    >CE-2.LAB(config)#in se 0/0:0
    >CE-2.LAB(config-if)#backup interface atm0/1
    >*Sep 6 13:24:43.174: %LINK-5-CHANGED: Interface ATM0/1, changed state to
    >standby mode
    >
    >Unfortunately this is 1:1 redundancy, i.e. you can't specify the same backup
    >interface for two primary interfaces. However, if all of your three lines
    >are of the same bandwidth and connected to the same routers, why don't you
    >just bundle them into multi-link PPP or do per-packet load-balancing across
    >all three lines?
    >
    >Kind regards,
    >iLya
    >
    yo, Mar 3, 2006
    #4
  5. yo

    Guest

    Charlie Root wrote:

    > Unfortunately this is 1:1 redundancy, i.e. you can't specify the same backup
    > interface for two primary interfaces. However, if all of your three lines
    > are of the same bandwidth and connected to the same routers, why don't you
    > just bundle them into multi-link PPP or do per-packet load-balancing across
    > all three lines?


    One semi-workaround to this problem with using one interface to backup
    two other interface might be to use the "backup load" command in
    addition to specifying the backup interface for one of the interfaces.
    That way, if the interface in the pair not being backed up went down,
    it would cause an increase in the load of the interface that does have
    a backup (but which is still up) and thus result in the the backup
    interface to come up for load reasons rather than for link failure if
    the threshold is set correctly.

    You would have to choose a somewhat high threshold for the load backup
    and decide the actual value based on heuristics from your knowledge of
    how heavily the two links are loaded on average. One problem might be
    that the backup interface might come up even if the other two
    interfaces are up but heavily loaded. Anyway, as mentioned, this is
    just a semi-workaround ...

    Cisco da Gama
    http://ciscostudy.blogspot.com
    , Mar 3, 2006
    #5
  6. yo

    Charlie Root Guest

    <yo> wrote in message news:...
    >
    > its a cost thing they dont want to load balance the 3rd line and only
    > want it as a backup solution.
    >


    ok, then the only solution I see is to use GRE tunnel between loopbacks of
    two routers, run EIGRP _only_ over the tunnel and have RTR tracker to setup
    route to the remote loopback over thirds interface only if one of the two
    "primary" links goes down. There will be slight overhead of GRE
    encapsulation and your routers CPU will be penalized, but at the moment I
    can't think of any alternative.

    I'm sorry, gotta go now. If you don't solve this issue during the weekend,
    I'll post configs with GRE on monday.

    Kind regards,
    iLya

    >
    >
    > On Fri, 3 Mar 2006 22:09:17 +0100, "Charlie Root"
    > <> wrote:
    >
    >><yo> wrote in message news:...
    >>> ok, im not sure if this is possible but if it is im sure someone here
    >>> knows how to get this working.
    >>>
    >>>
    >>> i have a router with 3 t1 links. im doing per packet load balancing on
    >>> the 1st 2 with the 3rd one being in admin down state and i only bring
    >>> it up when they need additional bandwidth.
    >>>
    >>> i want to conver this 3rd line into a fail over link, so that when one
    >>> of the 2 active load balancing lines goes down, the 3rd line will do
    >>> load balancing with the line that did not go down.
    >>>

    >>
    >>you could use 'backup interface <name_of_backup_interface>' command in
    >>primary interface configuration. Here is what happens:
    >>
    >>CE-2.LAB(config)#in se 0/0:0
    >>CE-2.LAB(config-if)#backup interface atm0/1
    >>*Sep 6 13:24:43.174: %LINK-5-CHANGED: Interface ATM0/1, changed state to
    >>standby mode
    >>
    >>Unfortunately this is 1:1 redundancy, i.e. you can't specify the same
    >>backup
    >>interface for two primary interfaces. However, if all of your three lines
    >>are of the same bandwidth and connected to the same routers, why don't you
    >>just bundle them into multi-link PPP or do per-packet load-balancing
    >>across
    >>all three lines?
    >>
    >>Kind regards,
    >>iLya
    >>

    >
    Charlie Root, Mar 3, 2006
    #6
  7. yo

    Charlie Root Guest

    <> wrote in message
    news:...
    > Charlie Root wrote:
    >
    >> Unfortunately this is 1:1 redundancy, i.e. you can't specify the same
    >> backup
    >> interface for two primary interfaces. However, if all of your three lines
    >> are of the same bandwidth and connected to the same routers, why don't
    >> you
    >> just bundle them into multi-link PPP or do per-packet load-balancing
    >> across
    >> all three lines?

    >
    > One semi-workaround to this problem with using one interface to backup
    > two other interface might be to use the "backup load" command in
    > addition to specifying the backup interface for one of the interfaces.
    > That way, if the interface in the pair not being backed up went down,
    > it would cause an increase in the load of the interface that does have
    > a backup (but which is still up) and thus result in the the backup
    > interface to come up for load reasons rather than for link failure if
    > the threshold is set correctly.
    >


    C-d-G, this is neat workaround. I didn't notice that now there is 'load'
    option now (used backup really long ago). If you don't mind I'd add some
    bits to your proposal - instead of backing up individual interface, get them
    into MLP bundle (only two links) and then backup will be for the whole
    bundle. I just tried - the backup command can be applied to Multilink
    interface, but I can't test until monday if it actually going to work.
    Though still as you've said choosing threshold values will require good
    quality crystal ball.

    Kind regards,
    iLya
    Charlie Root, Mar 3, 2006
    #7
  8. yo

    Charlie Root Guest

    "Charlie Root" <> wrote in message
    news:duaim1$103q$...
    > <yo> wrote in message news:...
    >>
    >> its a cost thing they dont want to load balance the 3rd line and only
    >> want it as a backup solution.
    >>

    >
    > ok, then the only solution I see is to use GRE tunnel between loopbacks of
    > two routers, run EIGRP _only_ over the tunnel and have RTR tracker to
    > setup route to the remote loopback over thirds interface only if one of
    > the two "primary" links goes down. There will be slight overhead of GRE
    > encapsulation and your routers CPU will be penalized, but at the moment I
    > can't think of any alternative.
    >
    > I'm sorry, gotta go now. If you don't solve this issue during the weekend,
    > I'll post configs with GRE on monday.
    >


    If it's still relevant, below is simplest version of possible config. Assume
    you have serial0/0:0 (IP: 192.168.0.2/30 on your side) and serial0/1:0 (IP:
    192.168.0.6/30) as two primary interfaces and serial1/0:0 is the backup
    interface (IP: 192.168.0.10/30); IP of the loopback (source of GRE tunnel)
    on the remote side is 192.168.1.1/32. The tunnel interfaces have addresses
    from other network though (say 192.168.130.0/30)

    !
    track 100 interface Serial0/0:0 line-protocol
    !
    track 101 interface Serial0/0:0 line-protocol
    !
    track 102 list boolean or
    object 100 not
    object 101 not
    !
    int lo0
    ip addr 192.168.1.2 255.255.255.255
    !
    int tun0
    ip addr 192.168.130.2 255.255.255.252
    tun mode gre
    tun source lo0
    tun dest 192.168.1.1
    !
    ip route 192.168.1.1 255.255.255.255 192.168.0.9 track 102
    !
    router eigrp 1
    network 192.168.130.0 0.0.0.3
    no auto-summary
    !

    CE-2.LAB#sh ip eigrp topology
    IP-EIGRP Topology Table for AS(1)/ID(192.168.129.2)

    Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
    r - reply Status, s - sia Status

    P 192.168.130.0/30, 1 successors, FD is 297244416
    via Connected, Tunnel0

    Add whatever other networks you have on these routers, but do NOT run EIGRP
    on serial interfaces (important!). The other side should configured in the
    similar fashion. If you want to have more reliable solution you just need to
    replace tracking interfaces with RTR ping probe of remote address like in
    this document -
    http://www.cisco.com/en/US/customer...3/products_feature_guide09186a00801d862d.html.

    I didn't have enough time to rebuild physical setup in the lab to represent
    the scenario, but here is some debug output that will give you an idea
    what's going on (disregard the addresses just watch out what's going on):

    CE-2.LAB# deb ip routing
    IP routing debugging is on
    CE-2.LAB#sh ip rou 192.168.1.1
    % Network not in table
    CE-2.LAB#conf t
    Enter configuration commands, one per line. End with CNTL/Z.
    CE-2.LAB(config)#int se0/0:0
    CE-2.LAB(config-if)#shut
    CE-2.LAB(config-if)#
    1w0d: is_up: 0 state: 6 sub state: 1 line: 0 has_route: True
    1w0d: RT: interface Serial0/0:0 removed from routing table
    1w0d: RT: del 192.168.128.20/30 via 0.0.0.0, connected metric [0/0]
    1w0d: RT: delete subnet route to 192.168.128.20/30
    1w0d: RT: NET-RED 192.168.128.20/30
    1w0d: RT: delete network route to 192.168.128.0
    1w0d: RT: NET-RED 192.168.128.0/24
    1w0d: RT: SET_LAST_RDB for 192.168.1.1/32
    NEW rdb: via 192.168.0.5

    1w0d: RT: add 192.168.1.1/32 via 192.168.0.5, static metric [1/0]
    1w0d: RT: NET-RED 192.168.1.1/32
    1w0d: RT: del 0.0.0.0 via 192.168.128.21, static metric [1/0]
    1w0d: RT: delete network route to 0.0.0.0
    1w0d: RT: NET-RED 0.0.0.0/0
    1w0d: RT: NET-RED 0.0.0.0/0
    *Sep 9 08:44:40.670: %LINK-5-CHANGED: Interface Serial0/0:0, changed state
    to administratively down
    1w0d: is_up: 0 state: 6 sub state: 1 line: 0 has_route: False
    *Sep 9 08:44:41.670: %LINEPROTO-5-UPDOWN: Line protocol on Interface
    Serial0/0:0, changed state to down
    1w0d: is_up: 0 state: 6 sub state: 1 line: 0 has_route: False^Z
    CE-2.LAB#sh ip rou 192.168.1.1
    *Sep 9 08:44:47.862: %SYS-5-CONFIG_I: Configured from console by console
    Routing entry for 192.168.1.1/32
    Known via "static", distance 1, metric 0
    Routing Descriptor Blocks:
    * 192.168.0.5
    Route metric is 0, traffic share count is 1

    CE-2.LAB#conf t
    Enter configuration commands, one per line. End with CNTL/Z.
    CE-2.LAB(config)#int se0/0:0
    CE-2.LAB(config-if)#no shut
    CE-2.LAB(config-if)#
    1w0d: is_up: 0 state: 4 sub state: 1 line: 0 has_route: False^Z
    CE-2.LAB#
    *Sep 9 08:45:02.778: %SYS-5-CONFIG_I: Configured from console by console
    *Sep 9 08:45:02.910: %LINK-3-UPDOWN: Interface Serial0/0:0, changed state
    to up
    1w0d: is_up: 1 state: 4 sub state: 1 line: 0 has_route: False
    1w0d: RT: SET_LAST_RDB for 192.168.128.20/30
    NEW rdb: is directly connected

    1w0d: RT: add 192.168.128.20/30 via 0.0.0.0, connected metric [0/0]
    1w0d: RT: NET-RED 192.168.128.20/30
    1w0d: RT: interface Serial0/0:0 added to routing table
    1w0d: is_up: 1 state: 4 sub state: 1 line: 0 has_route: True
    1w0d: RT: del 192.168.1.1/32 via 192.168.0.5, static metric [1/0]
    1w0d: RT: delete subnet route to 192.168.1.1/32
    1w0d: RT: NET-RED 192.168.1.1/32
    1w0d: RT: delete network route to 192.168.1.0
    1w0d: RT: NET-RED 192.168.1.0/24
    *Sep 9 08:45:04.074: %LINEPROTO-5-UPDOWN: Line protocol on Interface
    Serial0/0:0, changed state to up

    Hope this helps.

    Kind regards,
    iLya
    Charlie Root, Mar 6, 2006
    #8
  9. On Fri, 3 Mar 2006 22:09:17 +0100, "Charlie Root" <> wrote:

    ~ <yo> wrote in message news:...
    ~ > ok, im not sure if this is possible but if it is im sure someone here
    ~ > knows how to get this working.
    ~ >
    ~ >
    ~ > i have a router with 3 t1 links. im doing per packet load balancing on
    ~ > the 1st 2 with the 3rd one being in admin down state and i only bring
    ~ > it up when they need additional bandwidth.
    ~ >
    ~ > i want to conver this 3rd line into a fail over link, so that when one
    ~ > of the 2 active load balancing lines goes down, the 3rd line will do
    ~ > load balancing with the line that did not go down.
    ~ >
    ~
    ~ you could use 'backup interface <name_of_backup_interface>' command in
    ~ primary interface configuration. Here is what happens:
    ~
    ~ CE-2.LAB(config)#in se 0/0:0
    ~ CE-2.LAB(config-if)#backup interface atm0/1
    ~ *Sep 6 13:24:43.174: %LINK-5-CHANGED: Interface ATM0/1, changed state to
    ~ standby mode
    ~
    ~ Unfortunately this is 1:1 redundancy, i.e. you can't specify the same backup
    ~ interface for two primary interfaces. However, if all of your three lines
    ~ are of the same bandwidth and connected to the same routers, why don't you
    ~ just bundle them into multi-link PPP or do per-packet load-balancing across
    ~ all three lines?
    ~
    ~ Kind regards,
    ~ iLya
    ~

    One dialer profile can serve as a backup interface to multiple
    primary interfaces.
    Aaron Leonard, Mar 6, 2006
    #9
  10. yo

    Charlie Root Guest

    "Aaron Leonard" <> wrote in message
    news:...
    > On Fri, 3 Mar 2006 22:09:17 +0100, "Charlie Root"
    > <> wrote:
    >
    > ~ <yo> wrote in message news:...
    > ~ > ok, im not sure if this is possible but if it is im sure someone here
    > ~ > knows how to get this working.
    > ~ >
    > ~ >
    > ~ > i have a router with 3 t1 links. im doing per packet load balancing on
    > ~ > the 1st 2 with the 3rd one being in admin down state and i only bring
    > ~ > it up when they need additional bandwidth.
    > ~ >
    > ~ > i want to conver this 3rd line into a fail over link, so that when one
    > ~ > of the 2 active load balancing lines goes down, the 3rd line will do
    > ~ > load balancing with the line that did not go down.
    > ~ >
    > ~
    > ~ you could use 'backup interface <name_of_backup_interface>' command in
    > ~ primary interface configuration. Here is what happens:
    > ~
    > ~ CE-2.LAB(config)#in se 0/0:0
    > ~ CE-2.LAB(config-if)#backup interface atm0/1
    > ~ *Sep 6 13:24:43.174: %LINK-5-CHANGED: Interface ATM0/1, changed state
    > to
    > ~ standby mode
    > ~
    > ~ Unfortunately this is 1:1 redundancy, i.e. you can't specify the same
    > backup
    > ~ interface for two primary interfaces. However, if all of your three
    > lines
    > ~ are of the same bandwidth and connected to the same routers, why don't
    > you
    > ~ just bundle them into multi-link PPP or do per-packet load-balancing
    > across
    > ~ all three lines?
    > ~
    > ~ Kind regards,
    > ~ iLya
    > ~
    >
    > One dialer profile can serve as a backup interface to multiple
    > primary interfaces.


    Aaron,

    True, but in my experience Dialer profile does not go down, which then just
    replaces one problem with another. Dialer staying always up was the reason,
    why we started to use RTR-based tracking for setting up static routes
    conditionally. I haven't tried though Dialer with leased-line type
    interfaces.

    Kind regards,
    iLya
    Charlie Root, Mar 6, 2006
    #10
  11. ~ > One dialer profile can serve as a backup interface to multiple
    ~ > primary interfaces.
    ~
    ~ Aaron,
    ~
    ~ True, but in my experience Dialer profile does not go down, which then just
    ~ replaces one problem with another. Dialer staying always up was the reason,
    ~ why we started to use RTR-based tracking for setting up static routes
    ~ conditionally. I haven't tried though Dialer with leased-line type
    ~ interfaces.
    ~
    ~ Kind regards,
    ~ iLya

    Agreed, IP SLAs (nee RTR) is the most flexible approach.

    The original poster implied that he wanted to have his backup interface
    *down* (rather than just not transmitting traffic), which is why I was
    thinking dialers. I'm not sure if my inference was correct though ...
    Aaron Leonard, Mar 7, 2006
    #11
  12. yo

    Charlie Root Guest

    "Aaron Leonard" <> wrote in message
    news:...
    >
    > ~ > One dialer profile can serve as a backup interface to multiple
    > ~ > primary interfaces.
    > ~
    > ~ Aaron,
    > ~
    > ~ True, but in my experience Dialer profile does not go down, which then
    > just
    > ~ replaces one problem with another. Dialer staying always up was the
    > reason,
    > ~ why we started to use RTR-based tracking for setting up static routes
    > ~ conditionally. I haven't tried though Dialer with leased-line type
    > ~ interfaces.
    > ~
    > ~ Kind regards,
    > ~ iLya
    >
    > Agreed, IP SLAs (nee RTR) is the most flexible approach.
    >
    > The original poster implied that he wanted to have his backup interface
    > *down* (rather than just not transmitting traffic), which is why I was
    > thinking dialers. I'm not sure if my inference was correct though ...


    I hope you didn't get me wrong. I didn't mean to dismiss your proposed
    solution, neither to pretend that I understood original requirement
    correctly (importance whether actual state of the interface matters or only
    traffic mustn't pass). In fact now after re-reading your previous post it's
    obvious that you proposed to use dialer attached to the backup interface as
    opposed to binding several primary interface and then specify backup for
    dialer. Sorry for confusion.

    Kind regards,
    iLya
    Charlie Root, Mar 7, 2006
    #12
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