Document ID: 12019
This document discusses how to configure an Inter-Switch Link (ISL) Protocol trunk between a Cisco Catalyst 2948G-L3 and Catalyst 2900/3500XL or 2970 series switches. When you connect a Catalyst 2948G-L3 to a switch, the configuration tasks are the same as those to connect a router to a switch. The configuration example in this document uses the Catalyst 2948G-L3 as a router and uses the Catalyst 3500XL as the Layer 2 (L2) switch. You can substitute the Catalyst 2900XL or 2970 for the 3500XL, for the purposes of this document.
To use the concept of VLANs on the Catalyst 2948G-L3, you must use bridge groups. Each bridge group is considered a separate VLAN. These bridge groups correspond to the VLAN number of the connected switch.
Before you attempt this configuration, ensure that you connect a crossover cable between the 2900/3500XL or 2970 and the 2948G-L3. Typically, you use a straight-through cable between a router and a switch; but with the Catalyst 2948G-L3, you use a crossover cable to connect to another switch. This is the same crossover cable that you would use for a switch-to-switch connection.
Readers of this document should have knowledge of these topics:
The Catalyst 2940 and 2950/2955 series switches do not support ISL encapsulation. For information on ISL encapsulation support and other trunking requirements for Catalyst switches, refer to System Requirements to Implement Trunking.
The Catalyst 2948G-L3 has reached end of life (EoL). For details and recommended replacement products, refer to EoL / EoS for Cisco Catalyst 2948G-L3 and 4908G-L3 Switches.
The information in this document is based on these software versions:
Cisco IOS® Software Release 12.0(25)W5(27) for Layer 3 (L3) Switch/Router (CAT2948G-IN-M)
Cisco IOS Software Release 12.0(5)WC9 (C3500XL-C3H2S-M) (fc1)
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
For more information on document conventions, refer to the Cisco Technical Tips Conventions.
This section provides information to configure the features described in this document.
This document uses this network setup:
If you want all three PCs to be able to ping each other and have a default gateway, then you must use bridging with integrated routing and bridging (IRB).
The Catalyst 2948G-L3 is the L3 device in this scenario. Because it is an L3 device, it can not have two L3 interfaces in the same subnet. That is why you need to use bridge groups on the interfaces and tie them together with a bridge virtual interface (BVI), BVI 2.
The BVI 2 IP address is the default gateway for all of the PCs and devices in VLAN 2 or bridge group 2.
This document uses these configurations:
Building configuration... Current configuration: ! version 12.0 no service pad service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname 2948G-L3 ! ! ip subnet-zero bridge irb ! ! ! interface FastEthernet1 !--- This interface is the ISL trunk to the switch. no ip address no ip directed-broadcast ! interface FastEthernet1.1 encapsulation isl 1 no ip redirects no ip directed-broadcast bridge-group 1 !--- Use bridge-group 1 for the trunk subinterface. !--- You can not use an IP address here because of the subnet !--- overlap that would occur due to BVI 1, which is in the !--- same subnet. ! interface FastEthernet1.2 encapsulation isl 2 no ip redirects no ip directed-broadcast bridge-group 2 ! interface FastEthernet2 no ip address no ip directed-broadcast bridge-group 2 !--- This port belongs to VLAN 2. ! interface FastEthernet3 no ip address no ip directed-broadcast bridge-group 2 !--- This port belongs to VLAN 2. ! interface FastEthernet4 no ip address no ip directed-broadcast bridge-group 1 !--- This port belongs to VLAN 1. ! interface BVI1 ip address 10.1.1.1 255.255.0.0 !--- This is the IP address of BVI 1. no ip directed-broadcast no ip route-cache cef ! interface BVI2 !--- This is the IP address of BVI 2. ip address 10.2.2.2 255.255.0.0 no ip directed-broadcast no ip route-cache cef ! ip classless ! bridge 1 protocol ieee !--- Choose IEEE as the Spanning Tree Protocol. bridge 1 route ip !--- Allow routing to occur for IP. bridge 2 protocol ieee bridge 2 route ip ! line con 0 transport input none line aux 0 line vty 0 4 login ! end
|2900/3500XL or 2970|
!--- First, add VLAN 2 to the VLAN database for a 2900/3500XL !--- switch: 3500XL# vlan database 3500XL(vlan)# vlan 2 VLAN 2 added: Name: VLAN0002 3500XL(vlan)# exit APPLY completed. Exiting.... 3500XL# !--- The Catalyst 2970 gives you the option to configure VLANs !--- from the VLAN database or from global configuration mode: 2970# configure terminal Enter configuration commands, one per line. End with CNTL/Z. 2970(config)# vlan 2 2970(config-vlan)# end 2970#
!--- The switchport configurations on the Catalyst 2900/3500XL !--- and on the 2970 are identical, for the purposes of this !--- document. Remember that the Catalyst 2970 has 10/100/1000 !--- ports (1000Base-T), so the interfaces in this output !--- would instead be labeled Gigabit Ethernet 0/1, 0/2, !--- and so forth. Current configuration: ! version 12.0 no service pad service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname 3500XL ! interface FastEthernet0/1 switchport mode trunk !--- This port is an ISL trunk. ! interface FastEthernet0/2 switchport access vlan 2 !--- This port is in VLAN 2. ! interface FastEthernet0/3 !--- This port is in the default VLAN 1. ! interface FastEthernet0/4 ! ! interface VLAN1 ip address 10.1.1.100 255.255.0.0 !--- This is the IP address of the management interface. no ip directed-broadcast no ip route-cache ! snmp-server engineID local 000000090200000AF484CC80 snmp-server community public RO ! line con 0 exec-timeout 0 0 transport input none stopbits 1 line vty 0 4 login line vty 5 15 login ! end
This section provides information to confirm that your configuration is working properly.
show interface fa0/1 switchport—Verify the status of the trunk on the 2900/3500XL or 2970 and see which VLANs are active.
3500XL# show interface fa0/1 switchport Name: Fa0/1 Switchport: Enabled Administrative mode: trunk Operational Mode: trunk Administrative Trunking Encapsulation: isl Operational Trunking Encapsulation: isl Negotiation of Trunking: Disabled Access Mode VLAN: 0 ((Inactive)) Trunking Native Mode VLAN: 1 (default) Trunking VLANs Enabled: ALL Trunking VLANs Active: 1,2 Pruning VLANs Enabled: 2-1001 Priority for untagged frames: 0 Override vlan tag priority: FALSE Voice VLAN: none Appliance trust: none Self Loopback: No 3500XL#
show vlan—Verify that the ports on the 2900/3500XL or 2970 are assigned to the correct VLANs.
3500XL# show vlan VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 1 default active Fa0/3, Fa0/4, Fa0/5, Fa0/6, Fa0/7, Fa0/8, Fa0/9, Fa0/10, Fa0/11, Fa0/12, Fa0/13, Fa0/14, Fa0/15, Fa0/16, Fa0/17, Fa0/18, Fa0/19, Fa0/20, Fa0/21, Fa0/22, Fa0/23, Fa0/24, Gi0/1, Gi0/2 2 VLAN0002 active Fa0/2 1002 fddi-default active 1003 token-ring-default active 1004 fddinet-default active 1005 trnet-default active VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2 ---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------ 1 enet 100001 1500 - - - - - 0 0 2 enet 100002 1500 - - - - - 0 0 1002 fddi 101002 1500 - - - - - 0 0 1003 tr 101003 1500 - - - - - 0 0 1004 fdnet 101004 1500 - - - ieee - 0 0 1005 trnet 101005 1500 - - - ibm - 0 0 3500XL#
show interface bvi 1—Verify that the 2948G-L3 BVI interfaces and the line protocol are both up on the 2948G-L3.
2948G-L3# show interface bvi 1 BVI1 is up, line protocol is up Hardware is BVI, address is 0001.c75c.680a (bia 0000.0000.0000) Internet address is 10.1.1.1/16 MTU 1500 bytes, BW 10000 Kbit, DLY 5000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set ARP type: ARPA, ARP Timeout 04:00:00 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue 0/0 (size/max) 2948G-L3#
show bridge 1—Verify that bridge 1 is forwarding. You can also verify that Spanning Tree Protocol is enabled and forwarding with a show spanning-tree command.
2948G-L3# show bridge 1 Total of 300 station blocks, 299 free Codes: P - permanent, S - self Bridge Group 1: Address Action Interface 00ee.1e9f.50c0 forward Fa1.1 2948G-L3#
This section provides tips and sample output to help to troubleshoot your configuration.
Verify that you can ping across to the other device.
Verify that PCs can ping other PCs in other VLANs.
Ensure that the default gateway is correct. In this scenario, the default gateway is the respective BVIs on the 2948G-L3.
2948G-L3# ping 10.1.1.100 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.1.1.100, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/12 ms 2948G-L3# show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 10.2.2.2 - 0030.40d6.4008 ARPA BVI2 Internet 10.1.1.1 - 0030.40d6.400a ARPA BVI1 Internet 10.1.1.100 1 00ee.1e9f.50c0 ARPA BVI1 2948G-L3#
- LAN Product Support Pages
- LAN Switching Support Page
- Technical Support & Documentation - Cisco Systems
|Updated: Aug 30, 2005||Document ID: 12019|