192.168.10.10 Host 2 in VLAN150 with an
IP address of 192.168.150.3 Step 1 Verify
CEF. Verify that CEF is operational at global or interface
level using these commands: show ip cef summary
show
ip cef vlan 10 Note: CEF cannot be turned off on
most Cisco Catalyst platforms. If CEF is not operational, it is
likely that the Cisco Catalyst has disabled the feature. This
may be because of a software, feature, or hardware
incompatibility or inadequate memory to support a large FIB and
adjacency table. Step 2 Verify the configuration. If CEF
is not operational, display the running configuration to
determine whether any switching functions have been configured
that might disable CEF operations. If CEF is operational,
display the running configuration to verify the IP
configuration of the Layer 3 interfaces used for the hosts to
communicate. The IP addresses should be appropriate for the
subnet, and the interfaces should not be shut down. The
following is a sample of the configuration output expected for
the VLANs associated with the host communication. On this
router, VLAN 199 is the transit path that is traversed to
arrive at subnet 192.168.150.0: Switch#show running-config
interface VLAN 10
description Source VLAN
ip
address 192.168.10.1 255.255.255.0
!
interface VLAN
199
description Transit VLAN
ip address 192.168.199.1
255.255.255.0 Step 3 Verify the population of the
routing table on the route processor. The routing protocols and
route processor must populate the routing table accurately
before those routing table entries can be of use, because they
are transferred to the FIB to facilitate Layer 3 switching.
Verify the routing table by referring to a network diagram,
knowing which routes should appear in the routing table, and
then execute the show ip route command. In the case of
troubleshooting connectivity to the specific network of the
destination host (192.168.150.3/24), use the following
command: Switch#show ip route | include
192.168.150.0
O 192.168.150.0/24 [110/2] via
192.168.199.3, 00:13:00, VLAN 199 Step 4 The network is
accessible via the next-hop address 192.168.199.3. Therefore,
the ARP entry by which to access 192.168.150.3 should be the
MAC address resolved for 192.168.199.3. Verify an ARP entry on
the route processor. Verify that there is an ARP entry for the
next-hop IP address before checking whether that entry is
represented in the adjacency table. Switch#show ip arp
192.168.199.3
Protocol Address Age Hardware Addr Type
Interface
Internet 192.168.199.3 176 0030.7150.6800 ARPA
VLAN 199 Step 5 Verify the CEF FIB table entry for the
route. Step 3 verified that a route to network 192.168.150.0
existed in the routing table. Now verify that a CEF FIB entry
exists to that same destination to ensure that packets are
CEF-switched using the FIB rather than process-switched using
the routing table. Switch#show ip cef 192.168.150.0
192.168.150.0/24, version 298, cached adjacency 192.168.199.3
0 packets, 0 bytes
via 192.168.199.3, VLAN 199, 0
dependencies
next−hop 192.168.199.3, VLAN 199
valid cached adjacency This output verifies that there is a
valid CEF entry for the destination network. Packets can be
CEF-switched to the destination host. Step 6 Verify an
adjacency table entry for the destination. Verify that the FIB
entry shown in step 5 has an associated adjacency table entry
by using this command: Switch#show adjacency detail | begin
192.168.199.3
IP VLAN 199 192.168.199.3(7)
0
packets, 0 bytes
003071506800
.....
...
. The
above output indicates that there is an adjacency for the
next-hop IP address. The destination MAC address (003071506800)
is the MAC address in the ARP table, as displayed in step 4.
The counters (0 packets, 0 bytes) are almost always 0, since
packets are switched in hardware and, as such, they never reach
the route processor, which is required to increment counters.
Step 7 Verify CEF from the supervisor engine. The CEF
FIB and adjacency table entries shown in the example can also
be verified from the supervisor engine on modular switch
platforms, such as the 6500 series switches. This step is not
necessary on fixed configuration switches, such as the 3560. To
display an FIB entry for the specific network from the
supervisor engine: Console> (enable) show mls entry cef
ip 192.168.150.0/24
Mod FI-Type Destination-IP
Destination-Mask NextHop-IP Weight
--------------------------------------------------------------
15 resolved 192.168.150.0 255.255.255.255 192.168.199.3 1
To display an FIB entry for the specific network from the
supervisor engine:
Console> (enable) show mls entry
cef ip 192.168.150.0/24 adjacency
Mod:15
Destination-IP : 192.168.199.3 Destination-Mask :
255.255.255.255
FIB-Type : resolved
AdjType
NextHop-IP NextHop-Mac VLAN Encp TX-Packets
--------------------------------------------------------------
connect 192.168.199.3 00-30-71-50-68-00 199 ARPA 0
Content 4.4 Inter-VLAN Routing Lab Exercises
4.4.1 Lab 4-1 Inter-VLAN Routing with an External
Router Lab Activity Lab Exercise: Lab 4-1
Inter-VLAN Routing with an External Router This lab configures
inter-VLAN routing using an external router, also known as a
router-on-a-stick.
Content 4.4 Inter-VLAN
Routing Lab Exercises 4.4.2 Lab 4-2 Inter-VLAN
Routing with an Internal Route Processor and Monitoring CEF
Functions Lab Activity Lab Exercise: Lab 4-2
Inter-VLAN Routing with an Internal Route Processor and
Monitoring CEF Functions This lab routes between VLANs using a
3560 switch with an internal route processor using Cisco
Express Forwarding (CEF).
Content Summary The
configuration of multiple VLANs usually requires that Layer 3
routing occurs between those VLANs. This inter-VLAN routing can
be provided external to a Layer 2 switch or within a multilayer
switch through the configuration of Switch Virtual Interfaces
(SVIs) and IP routing. When routing occurs within a Cisco
Catalyst multilayer switch, Cisco Express Forwarding (CEF) is
deployed to facilitate Layer 3 switching through
hardware-based tables, providing an optimal packet-forwarding
process.