View source for CCNP Equal Cost Multi Path (ECMP)

Intro
=Routing - Verifying CEF's 15 hash-buckets=
Verification of Configuration
<pre>
Leaf-1#show ip route
Gateway of last resort is not set


      10.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
C        10.1.1.0/24 is directly connected, gig0/1
L        10.1.1.1/32 is directly connected, gig0/1
C        10.2.2.0/24 is directly connected, gig0/2
L        10.2.2.1/32 is directly connected, gig0/2
C        10.3.3.0/24 is directly connected, gig0/3
L        10.3.3.1/32 is directly connected, gig0/3
</pre>

Note above that we have one subnet for each spine switch 


 O        10.2.0.0/16  [110/2] via 10.1.1.3, 1d19h, gig0/1   ← Assuming we add summary
                       [110/2] via 10.2.2.3, 1d19h, gig0/2
                       [110/2] via 10.3.3.3, 1d19h, gig0/3
 O        10.3.0.0/16  [110/2] via 10.1.1.3, 1d19h, gig0/1   ← Assuming we add summary
                       [110/2] via 10.2.2.3, 1d19h, gig0/2
                       [110/2] via 10.3.3.3, 1d19h, gig0/3
 O        10.4.0.0/16  [110/2] via 10.1.1.3, 1d19h, gig0/1   ← Assuming we add summary
                       [110/2] via 10.2.2.3, 1d19h, gig0/2
                       [110/2] via 10.3.3.3, 1d19h, gig0/3
Note above that we have three equal cost paths to servers on other leafs, the same amount of parallel paths as we have spines. 


 C        10.1.10.0/30 is directly connected, gig0/10
 L        10.1.10.1/32 is directly connected, gig0/10
 C        10.1.11.0/30 is directly connected, gig0/11
 L        10.1.11.1/32 is directly connected, gig0/11
 C        10.1.12.0/30 is directly connected, gig0/12
 L        10.1.12.1/32 is directly connected, gig0/12
 
Note above that every server is in its own LAN, with 10.$leaf.$down_port.1 as default-gateway. ($y ??)


Now we check the hash-buckets for load balancing over spines/between leafs.
 Leaf-4#show ip cef 10.5.0.0 internal
 10.5.0.0/16, epoch 3, RIB[I], refcount 6, per-destination sharing
   sources: RIB
   feature space:
    Broker: linked, distributed at 4th priority
   ifnums:
    FastEthernet0/1(469): 10.1.1.5
    FastEthernet0/2(470): 10.2.2.5
    FastEthernet0/2(470): 10.3.3.5
   path 0625780C, path list 053A00B0, share 1/1, type attached nexthop, for IPv4
   nexthop 10.1.1.5 gig0/1, adjacency IP adj out of gig0/1, addr 10.1.1.5 058EF420
   path 0625787C, path list 053A00B0, share 1/1, type attached nexthop, for IPv4
   nexthop 10.2.2.5 gig0/2, adjacency IP adj out of gig0/2, addr 10.2.2.5 058EF280
   path 0625787C, path list 053A00B0, share 1/1, type attached nexthop, for IPv4
   nexthop 10.3.3.5 gig0/2, adjacency IP adj out of gig0/2, addr 10.2.2.5 05EFAKE0
  
 
   output chain:
     loadinfo 0588EE68, per-session, 2 choices, flags 0003, 6 locks
     flags: Per-session, for-rx-IPv4
     16 hash buckets
      < 0 > IP adj out of FastEthernet0/1, addr 10.1.1.3 058EF420
      < 1 > IP adj out of FastEthernet0/2, addr 10.2.2.3 058EF280
      < 2 > IP adj out of FastEthernet0/3, addr 10.1.1.3 058FAKE0
      < 3 > IP adj out of FastEthernet0/1, addr 10.2.2.3 058EF420
      < 4 > IP adj out of FastEthernet0/2, addr 10.1.1.3 058EF280
      < 5 > IP adj out of FastEthernet0/3, addr 10.2.2.3 058FAKE0
      < 6 > IP adj out of FastEthernet0/1, addr 10.1.1.3 058EF420
      < 7 > IP adj out of FastEthernet0/2, addr 10.2.2.3 058EF280
      < 8 > IP adj out of FastEthernet0/3, addr 10.1.1.3 058FAKE0
      < 9 > IP adj out of FastEthernet0/1, addr 10.2.2.3 058EF420
      <10 > IP adj out of FastEthernet0/2, addr 10.1.1.3 058EF280
      <11 > IP adj out of FastEthernet0/3, addr 10.2.2.3 058FAKE0
      <12 > IP adj out of FastEthernet0/1, addr 10.1.1.3 058EF420
      <13 > IP adj out of FastEthernet0/2, addr 10.2.2.3 058EF280
      <14 > IP adj out of FastEthernet0/3, addr 10.1.1.3 058FAKE0
      <15 >  -- not used /Robert
    Subblocks:
     None
 Leaf-4#

Sometimes you need to tweak the load balancing scheme with the command
  ip cef load-sharing algorithm include-ports source destination

Done! 
 Congratulations.
= Routing - Verifying path in CEF=
<font color=RED>This has not been verified for L3 Etherchannels</font>
 show ip cef exact-route source-ip-address destination-ip-address
Example from [http://packetlife.net/blog/2011/may/27/show-ip-cef/ http://packetlife.net/blog/2011/may/27/show-ip-cef/]
 Router# show ip cef exact-route 10.0.9.5 192.168.0.1
 10.0.9.5        -> 192.168.0.1    : FastEthernet0/1 (next hop 10.0.9.18)
 Router# show ip cef exact-route 10.0.9.6 192.168.0.1
 10.0.9.6        -> 192.168.0.1    : FastEthernet0/0 (next hop 10.0.9.14)

Source: [http://www.netcraftsmen.com/load-balancing-and-cisco-express-forwarding-cef-with-parallel-paths/ http://www.netcraftsmen.com/load-balancing-and-cisco-express-forwarding-cef-with-parallel-paths/]

=CEF with EtherChannel=
From: [http://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html#catalyst Understanding EtherChannel Load Balancing and Redundancy on Catalyst Switches] paragraph [http://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html#catalyst Catalyst 3560]

You can find out which interface is used in the EtherChannel to forward traffic based on <br>
the load balancing method. The command for this determination is 
 test etherchannel load-balance interface port-channel number {ip | mac} [source_ip_add | source_mac_add] [dest_ip_add | dest_mac_add]

Example:


----------------
 switch#'''show ip cef exact-route 172.16.79.186 192.168.42.183'''
 172.16.79.186 -> 192.168.42.183 => IP adj out of Vlan100, addr 10.10.1.245 
 
 switch#'''show vlan id 100'''
 VLAN Name Status Ports
 ---- -------------------------------- --------- -------------------------------
 100 uplink1 active Po4


 switch#'''test etherchannel load-balance interface po4 ip 172.16.79.186 192.168.42.183'''
 Would select Gi0/51 of Po4

 switch#'''show controller util | inc (^Port|Gi0/51)'''
 Port Receive Utilization Transmit Utilization
 Gi0/51 1 0 

Example 2:
 switch#'''show control util'''
 Port Receive Utilization Transmit Utilization
 Gi0/49 1 55
 Gi0/50 6 0
 Gi0/51 1 0
 Gi0/52 12 57 

== Debugging according to Cisco==
Regular Interface (No Subinterfaces) 
<pre>
Step 1
View the Address Resolution Protocol (ARP).
RP/0/RSP0/CPU0:router# show arp 

Step 2
Verify that the lag table is programmed properly in the hardware.
RP/0/RSP0/CPU0:router# show interface bundle-ether bundle-id 

Step 3
View the running configuration information.
RP/0/RSP0/CPU0:router# show running-config 

Step 4
View information about packets forwarded by CEF.
RP/0/RSP0/CPU0:router# show cef 

Step 5
RP/0/RSP0/CPU0:router# show cef hardware ingress location node-id

Step 6
RP/0/RSP0/CPU0:router# show cef hardware egress location node-id 

'''Subinterface''' 

Step 1
Troubleshoot Layer 3 IPv4 traffic.
Step 2
Ensure that VLAN traffic coming in matches that on the incoming interface.

Ping Failed over Bundle
Step 1
View the ARP.
RP/0/RSP0/CPU0:router# show arp 
Step 2
View the ARP information on the particular LC or RSP.
RP/0/RSP0/CPU0:router# show arp location node-id
Step 3
RP/0/RSP0/CPU0:router# show cef hardware detail location node-id ingress 
Step 4
RP/0/RSP0/CPU0:router# show interface 
Step 5
Use the hash calculator to determine which bundle member (interface) to test.
Step 6
Remove the interface from the bundle.
Step 7
Assign an IP address to the interface.
Step 8
Ping the interface.
Step 9
Ensure that the ARP is resolved between the router and the node being pinged.
### END ###
</pre>

=dCEF=
Brandon,
Just as a side note, "show ip cef exact-route" will show you the
software CEF hash. It's not useful on hardware platforms to determine
path selection as hardware will not necessarily make the same
decision. "'''show mls cef exact-route'''" is what you want to use on these
platforms. For distributed forwarding(DFC) platforms it may need to be
checked by attaching to the ingress LC.

-Ben 
[http://www.gossamer-threads.com/lists/cisco/nsp/140211 http://www.gossamer-threads.com/lists/cisco/nsp/140211]

=NEXT2=
bbb
=NEXT3=

hej.