Transcript InterVLAN Routing - YSU Computer Science & Information Systems

InterVLAN Routing
Design and Implementation
What Routers Do
• Intelligent, dynamic routing protocols for
packet transport
• Packet filtering capabilities
• Connectivity enhancements – DHCP, NAT,
QoS, policy-based routing
• Connectivity between LAN and WAN
Routing Issues
• Isolated broadcast domains
– Linked by routers (Layer 3)
• Sending nonlocal packets
– Routing protocols, gateway of last resort,
default routes
• Supporting multiple VLAN packets across
VLAN boundaries
– ISL solves problem
ISL
• Supported over Fast Ethernet links
– Single ISL link (trunk) can carry traffic from
multiple VLANs
• Packets encapsulated with ISL VLAN header
appropriate to destination and routes to appropriate
interface
Routing in a Switched Network
• interVLAN routing
– Add a route processor in switched network to provide layer 3
routing
• Every packet goes through the router
• Layer 3 switching (RSM- route switch module)
– Router running IOS software plugs into switch backplane
• Appears as module with single 800 Mb half duplex trunk port and one
MAC address
• Multilayer switching (MLS)
– Router sees only first packet; sets up switching paths to bypass the
router
• Cisco Express Forwarding (CEF)
– Distributed switching mechanism
RSM Details
• Provides multilayer switching and interVLAN routing between switched VLANs
– Can be installed in slots 2 through 12
– Maximum number of modules is 7 for Cat 5500
– RSM is mapped through VLAN 0 and VLAN 1
• VLAN 0 to channel 0; VLAN 1 to channel 1
• VLAN 0 assigned ROM MAC address
• VLAN 1 assigned base MAC address from 512
available MAC addresses
Routing with Multiple Physical
Links
• Use one link for each VLAN on switch to connected router
– Each packet travels across a link reserved for VLAN
traffic
• Useful when switches and router are already available and can
be quickly connected
• Not a good idea to use when network grows
• Trunk links
– Use only one link to router – router on a stick or onearmed router
• Integrated Router
– Route processor is inside the switch for tighter
integration of layer 2 and layer 3 components
Routing Over Trunk Lines
• 802.1q and ISL trunks
– Use Fast Ethernet or Gigabit Ethernet
– Each frame identified with VLAN number
• Frame encapsulated as it leaves switch
– Offer scalability because single link can
transport many VLANs
– Requires link bandwidth overhead
• 30-byte header (ISL) or 4-byte header (802.1q)
Routing with an Integrated
Router
• Route Switch Module (RSM)
– Runs Cisco ISO software
– Interfaces to switch through backplane – channel 0 and
channel 1
• Route processor is module with route switch in the moduletype field
– Use show module command
– Use session to telnet from switch to router
• Multilayer Switch Feature Card (MSFC)
– Shortcuts switch layer 3 and higher protocols – to be
covered in detail later
VLAN Connectivity and Trunk
lines
• (config)# int 2/3.1
• (config-if)#encap isl vlan2
• Ip address n.n.n.n s.s.s.s
– Each subinterface is assigned to specific VLAN
– VLAN numbers should match on both router
and switch ends
Routing Processes
• Route processor keeps local table of known routes,
metrics, interfaces, and neighboring routers
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Uses dynamic routing protocols and static routes
(config)# ip routing
(config)# router rip
(config-router)# network n.n.n.n
• Switch (enable) set ip route default gateway