FR multipoint interfaces

Guys i must say i really thank all guys who helped me for my previous FR question...you all are amazing.....my final glitch in FR is that

if i have three sites i can confoig framerelay as hub in spoke

so physical link will have two DLCI (no point to point or multipoint) and spoke can have DLCI and i can do static maping on all three routers and they will all work i can turn off split horizon on th ephysical so that one spoke can reach other spoke if that is the case why would i make point to multipoint (sub interfaces) on the router serial....what is the difference between config DLCI on physical (map) and making sub interfaces both will work same way...(if there is a same subnet) i know for point to point different subnets can be used so it malke scence why would i make point to multipoint as i can do it with making sub interfaces

 

Thanks again

 

Comments

  • Actually it is based on type of protocols you want to run over. Yes Point to Point means separate subnet but some time we need this to resolve some multicast issues.

    But according to your scenario:

    There is no difference of mapping on physical interface or on subinterface.

    See here

    R1#show running-config interface serial 0/0
    Building configuration...

    Current configuration : 216 bytes
    !
    interface Serial0/0
     ip address 192.168.0.1 255.255.255.0
     encapsulation frame-relay
     serial restart-delay 0
     frame-relay map ip 192.168.0.3 103
     frame-relay map ip 192.168.0.4 104
     no frame-relay inverse-arp

    !

    R1#ping 192.168.0.3

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 192.168.0.3, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 36/56/108 ms
    R1#ping 192.168.0.4

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 192.168.0.4, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 28/67/116 ms

    I am reachable to all Spoke

    R4#ping 192.168.0.3

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 192.168.0.3, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 72/104/192 ms

    One spoke also reachable to another spoke because I have mapping to another spoke and to hub

    Let's create multipoint subinterface on HUB:

    R1#show running-config interface s0/0.100
    Building configuration...

    Current configuration : 152 bytes
    !
    interface Serial0/0.100 multipoint
     ip address 192.168.0.1 255.255.255.0
     frame-relay map ip 192.168.0.3 103
     frame-relay map ip 192.168.0.4 104

    !

    R1#show running-config int s0/0.100
    Building configuration...

    Current configuration : 152 bytes
    !
    interface Serial0/0.100 multipoint
     ip address 192.168.0.1 255.255.255.0
     frame-relay map ip 192.168.0.3 103
     frame-relay map ip 192.168.0.4 104
    end
    !

    R1#ping 192.168.0.4

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 192.168.0.4, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 36/63/120 ms
    R1#ping 192.168.0.3

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 192.168.0.3, timeout is 2 seconds:
    !!!!!

    [:D]

  • As nnn mentioned it depends on the routing protocol. However physical FR encapsulated interfaces and FR multipoint subinterfaces have slightly different default behaviors.

    For instance, physical FR interfaces have split horizon automatically disabled while multipoint subinterfaces have split horizon on:

    1#sh run int s5/0
    Building configuration...

    Current configuration : 242 bytes
    !
    interface Serial5/0
     ip address 10.0.0.1 255.255.255.0
     encapsulation frame-relay
     no fair-queue
     serial restart-delay 0
     frame-relay map ip 10.0.0.3 101 broadcast
     frame-relay map ip 10.0.0.2 100 broadcast
     no frame-relay inverse-arp
    end

    R1#sh ip int s5/0 | i Spli
      Split horizon is disabled

    -------

    R3#sh run int s5/0
    Building configuration...

    Current configuration : 121 bytes
    !
    interface Serial5/0
     no ip address
     encapsulation frame-relay
     serial restart-delay 0
     no frame-relay inverse-arp
    end

    R3#sh run int s5/0.1
    Building configuration...

    Current configuration : 151 bytes
    !
    interface Serial5/0.1 multipoint
     ip address 10.0.0.3 255.255.255.0
     frame-relay map ip 10.0.0.2 300
     frame-relay map ip 10.0.0.1 300 broadcast
    end

    R3#sh ip int s5/0.1 | i Spli
      Split horizon is enabled

    See here for FR FAQs:

    http://www.cisco.com/en/US/tech/tk713/tk237/technologies_q_and_a_item09186a008009457a.shtml

  • You are correct Soul,

    R1#show ip int s0/0.100 | in Split
      Split horizon is enabled
    !
    R1#show ip int s0/0 | in Split
      Split horizon is disabled

    [:D]

  • In short "Split Horizon" has nothing to do with Frame Relay itself. Split horizon is a behavior which we see in Distance Vector Routing protocols. Also routing protocol such as RIP has SPLIT HORIZON disabled by default for Physical FR Multipoint Interfaces. On the other hand for EIGRP it's enabled. Little tweak about EIGRP though is that you can only see if split horizon is enabled or disabled for a particular interface by looking at "SH RUN" as " sh ip int " won't help here.

    Now as far type of FR interface goes, it's more of a design that pretty much choose which one will be used. Also FR is a legacy technology, so you  can find some thing like FR on edge of SP network and MPLS in SP CORE network.

    As far I have seen, people usually preffer FR P2P interfaces in real world to avoid any potential issues.

     

    HTH...

    Deepak Arora

    http://deepakarora1984.blogspot.com

     

     

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