CCNP Equal Cost Multi Path (ECMP)
From Datateknik
Intro
Contents |
Routing - Verifying CEF's 15 hash-buckets
Verification of Configuration
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
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
This has not been verified for L3 Etherchannels
show ip cef exact-route source-ip-address destination-ip-address
Example from 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/
CEF with EtherChannel
From: Understanding EtherChannel Load Balancing and Redundancy on Catalyst Switches paragraph Catalyst 3560
You can find out which interface is used in the EtherChannel to forward traffic based on
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:
6509-sp#test etherchannel load-balance interface port-channel 1 mac 00d0.c0d7.2dd4 0002.fc26.2494 Would select Gi6/1 of Po1 6509-sp#
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)
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 ###
On 6500--PFC-3C system with src-dst-ip enhanced algorithm:
PFC-3C#show etherchannel load-balance hash-result interface port-channel 1 ip 10.1.1.1 vlan 10 10.2.2.2 Computed RBH: 0x1 Would select Gig3/2 of Po1
In the end let me just share with you command to verify transmitters of Catalyst 4500 and 2k/3k respectively:
“show platform software etherchannel port-channel 5 map ip 1.1.1.1 1.1.1.2” “test etherchannel load-balance interface port-channel 1 ip 1.1.1.1 1.1.1.2”
From: packetpushers.net
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
First Try on 7609 to 6504, 10 GBE
Leaf3-7609#
Leaf3-7609#show ip cef exact 10.33.33.33 10.11.11.11 detail
10.33.33.33 -> 10.11.11.11 : TenGigabitEthernet8/1 (next hop 10.1.1.1)
Leaf3-7609#
Leaf3-7609#show ip cef exact 10.33.33.33 10.11.11.11
10.33.33.33 -> 10.11.11.11 : TenGigabitEthernet8/1 (next hop 10.1.1.1)
Leaf3-7609#
Leaf3-7609#show running | beg ospf
router ospf 1
log-adjacency-changes
network 10.0.0.0 0.255.255.255 area 0
!
!
interface TenGigabitEthernet8/1
ip address 10.1.1.3 255.255.255.0
end
Leaf3-7609#
Leaf3-7609#show ip cef state
^
% Invalid input detected at '^' marker.
Leaf3-7609#show ip cef ?
A.B.C.D prefix of entries to show
Async Async interface
CTunnel CTunnel interface
Dialer Dialer interface
GigabitEthernet GigabitEthernet IEEE 802.3z
Group-Async Async Group interface
Loopback Loopback interface
MFR Multilink Frame Relay bundle interface
Multilink Multilink-group interface
Null Null interface
Port-channel Ethernet Channel of interfaces
Pos-channel POS Channel of interfaces
TenGigabitEthernet Ten Gigabit Ethernet
Tunnel Tunnel interface
Vif PGM Multicast Host interface
Virtual-Template Virtual Template interface
Virtual-TokenRing Virtual TokenRing
Vlan Catalyst Vlans
XTagATM Extended Tag ATM interface
adjacency Display all prefixes resolving through adjacency
detail Display full information
epoch Display epoch information
events Show CEF table events
exact-route Display exact route for a session
fcpa Fiber Channel
inconsistency Show table inconsistency information
non-recursive Display non-recursive routes only
summary CEF table summary
traffic Display traffic statistics
unresolved Display unresolved routes only
vrf Show VPN Routing/Forwarding instance CEF table
| Output modifiers
<cr>
Leaf3-7609#show ip cef 10.33.33.33 ?
A.B.C.D prefix mask
detail Display full information
| Output modifiers
<cr>
Leaf3-7609#
Leaf3-7609#show fabric switching-mode
Global switching mode is Compact
dCEF mode is not enforced for system to operate
Fabric module is not required for system to operate
Modules are allowed to operate in bus mode
Truncated mode is allowed, due to presence of DFC, CEF720, Standby supervisor module
Module Slot Switching Mode
2 Crossbar
3 Crossbar
4 Crossbar
5 dCEF
6 Crossbar
8 dCEF
Leaf3-7609#
Leaf3-7609#
Leaf1-6504#
1 dCEF
2 Crossbar
3 Crossbar
'''4 Crossbar'''
Interface Ten sitter i bladplats 4
Polarization
Be The Packets – CCIE Study Blog
Review/Perspective: CEF Concepts
- 1.1.b Identify Cisco express forwarding concepts
- 1.1.b [i] RIB, FIB, LFIB, Adjacency table
- 1.1.b [ii] Load balancing Hash
- 1.1.b [iii] Polarization concept and avoidance
