Load-balancing across four T1's on 2 routers

Discussion in 'Cisco' started by Sean-Usenet, Aug 31, 2006.

  1. Sean-Usenet

    Merv Guest

    Perhaps you could use .1Q trunking between the 2800 routers and the
    layer 3 switch.

    On each 2800 define two sub-interfaces on the FastEthernet major
    interface - 1 for each T1 - if a T1 is up advertise only the default
    route for that T1 over the corresponding FE sub-interface (VLAN) to the
    layer 3 switch.

    If all four T1 are up, the layer 3 switch will have 4 default routes
    and will load balance on a per destination basis over these four
    routes.

    Need to figure out if reliable static routing using object tracking or
    something similiar can accomplish the above routing scenario.
     
    Merv, Sep 1, 2006
    #21
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  2. Sean-Usenet

    Merv Guest

    What is the make and model of the layer 3 switch

    If it is Cisco what is the IOS version ?
     
    Merv, Sep 1, 2006
    #22
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  3. Sean-Usenet

    Sean-Usenet Guest

    It is a Cisco 3750 switchstack running the latest - 12.2(25)SEE2
     
    Sean-Usenet, Sep 1, 2006
    #23
  4. Sean-Usenet

    Sean-Usenet Guest

    Interesting idea. I'll have to see if i can do something like that.

    Thanks!
    Sean
     
    Sean-Usenet, Sep 1, 2006
    #24
  5. Sean-Usenet

    Merv Guest

    Is there any flexibility with respect to the IGP routing protocol ?

    Which routing protcols will your ISP support over your T1 links ?

    What IOS is/will be used on the 2800 's ?

    BTW how does the ISP intend to deal with this issue as it affects your
    inbound traffic ???
     
    Merv, Sep 1, 2006
    #25
  6. Sean-Usenet

    Merv Guest

    Merv, Sep 1, 2006
    #26
  7. Sean-Usenet

    Merv Guest

    OBTW it is possible to support ECMP with BGP, the magic knob is max
    paths

    router bgp <AS>
    maximum-paths eibgp 4
     
    Merv, Sep 1, 2006
    #27
  8. Sean-Usenet

    nakhmanson Guest

    Sean

    Thanks for the reply, but now it's even more "puzzling". Just out of
    curiosity, since you have everything redundant (2 routers from an ISP +
    2 switches + firewall with failover) why ONE ISP? ;-)
    Sure.
    With your current setup, I'd get rid of L3 pair and use OSPF on the
    firewall (assuming it's a Cisco pix failover pair with more or less new
    version).
    You are absolutely right. And as always there is a "BUT"
    Most likely client will be using just ONE T1 for any current session,
    unless you do some "serious magic" like "per-packet" or "no ip
    load-sharing per-destination". And some times people just want to
    download stuff faster then 180kB/s. If you would use MLPP - any given
    session is capable of getting up to 360kB/s guaranteed. And yes, if you
    lose a T1 - you lose the "whole" router because of OSPF. But there are
    always other ways of doing things (keeping in mind that T1 would be
    fixed within reasonable period of time). For example you can use BGP
    with link bandwidth feature between you and ISP. (using EIGRP between
    you and ISP would be unconventional, but possible). Or even better
    scenario - get two ISP with 2 T1 each. MLPP with each ISP. BGP (default
    + local routes) towards you from each ISP. GLBP/HSRP/VRRP or OSPF on
    routers.

    just my 2c
    Roman
     
    nakhmanson, Sep 1, 2006
    #28
  9. Sean-Usenet

    Sean-Usenet Guest

    Hi Roman

    On the one ISP thing, that is just how they want it - this is just a
    small contract job i'm doing.

    My experience is mainly related to OSPF not BGP. I'll start looking at
    BGP, it sounds like it may be a better fit? If you have any pointers
    on setting it up using BGP let me know!

    Thanks
    Sean
     
    Sean-Usenet, Sep 1, 2006
    #29
  10. Sean-Usenet

    Sean-Usenet Guest

    There is probably some flexiblity in regards wo which IGP routing
    protocol we use.

    Do you think a different routing protocol would work better in this
    scenario?

    The 2800's will run the latest 12.4 IOS
     
    Sean-Usenet, Sep 1, 2006
    #30
  11. Sean-Usenet

    Sean-Usenet Guest

    They might, although I'll have to do some quick reading on BGP, as my
    routing experience is mainly OSPF.

    I'll check out the link, if you have any pointers on how to set this up
    using BGP let me know!

    Thanks again for your help
    Sean
     
    Sean-Usenet, Sep 1, 2006
    #31
  12. Sean-Usenet

    Merv Guest

    I would defintiely use BGP if I were implementing this network
    scenario.

    BGP via route maps provides a great dealing of flexiibility with
    respect to route manipulation and filtering. Filtering routes in OSPF
    can only be done in some special cases.

    BGP has the ability to do equal cost multi-path load balancing (
    requires configuration). It would allow you to address the issue I
    raised about getting blackholed if the ISP access router becomes
    partitioned, etc, etc.

    BGP has the ability to establish its TCP session thru a firewall and
    this is must useful in case of having two active firewalls.

    The ISP can advertise just default or default + the ISP routes (ie
    ..partial BGP routes).

    If you need to change ISP providers in the future the new provider
    might not be willing to support OSPF. ALL ISP's that I have encountered
    will support BGP.


    I would also take another look at MLPPP - at least find out if the ISP
    will support.
     
    Merv, Sep 1, 2006
    #32
  13. Sean-Usenet

    nakhmanson Guest

    Sean

    In you case (one ISP) BGP scenario will be really easy.
    You will have a luxury of using BGP on low-end boxes just because you
    need only default from your provider. Also (as Merv pointed earlier)
    you need "maximum-paths" configured

    Something like this (for v12.4):

    router bgp <private AS number that ISP and you agreed upon>
    bgp log-neighbor-changes
    neighbor <ip of the first T1 ISP router1> remote-as <AS number of you
    ISP>
    neighbor <ip of the second T1 ISP router2 or router1> remote-as <AS
    number of you ISP>
    maximum-paths 4

    address-family ipv4
    neighbor <ip of the T1 ISP router1> activate
    neighbor <ip of the T1 ISP router2 or router1> activate
    no auto-summary
    no synchronization
    network <"your" subnet> mask <"your" mask> {your provider will
    decide about your BGP route announce}
    exit-address-family


    In case of MLPP use - here is the link
    http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t2/ftbgplb.htm


    Roman Nakhmanson
     
    nakhmanson, Sep 1, 2006
    #33
  14. Sean-Usenet

    Sean-Usenet Guest

    Great, thanks for the detailed information. Does BGP support
    UNequal-cost load-balancing? Something like if we lose one T1, one
    router will receive 2/3 of the traffic and the other will receiving 1/3
    of the traffic?

    EIGRP supports UNequal-cost load-balancing in that manner, what do you
    think about a solution using EIGRP and MLPP?
     
    Sean-Usenet, Sep 1, 2006
    #34
  15. Sean-Usenet

    nakhmanson Guest

    Sean
    Yes, just add couple more command to your BGP config
    http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t2/ftbgplb.htm
    EIGRP between you and ISP? Not a good practice, but possible
    It's OK to use MLPP between you and ISP anyway, especially if you have
    BGP load bandwidth configured

    If you have 2 routers with multilink connection (2 T1 bundle)
    Your BGP part would be something like this:

    router bgp <private AS number that ISP and you agreed upon>
    bgp log-neighbor-changes
    neighbor <ip of the first multilink ISP router1> remote-as <AS number
    of your ISP>
    neighbor <ip of your router2> remote-as <private AS number that ISP and
    you agreed upon>
    maximum-paths 2

    address-family ipv4
    bgp dmzlink-bw
    neighbor <ip of the T1 ISP router1> activate
    neighbor <ip of the T1 ISP router1> dmzlink-bw
    neighbor <ip of your router2> activate
    neighbor <ip of your router2> next-hop-self
    neighbor <ip of your router2> send-community both
    no auto-summary
    no synchronization
    network <"your" subnet> mask <"your" mask> {your provider will decide
    about your BGP route announce}
    exit-address-family


    Roman Nakhmanson
     
    nakhmanson, Sep 1, 2006
    #35
  16. Sean-Usenet

    Merv Guest

    It is not clear that when a link within an MLPPP bundle drops, that the
    BGP link bandwidth feature woud re-advertise all the affected external
    routes to its internal BGP neighbours.

    Since the EBGP external link bandwidth are carried within extended
    communities this would have to occur in order for the iBGP neighbors to
    load bancing accordingly.
     
    Merv, Sep 2, 2006
    #36
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