Brocade Communications Systems Brocate Ethernet Access Switch 6910 - Manual (Page 1093)

Brocade 6910 Ethernet Access Switch Configuration Guide 1043
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Configuring IP Routing Interfaces
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If the destination belongs to a different subnet on this switch, the packet can be routed directly to
the destination node. However, if the packet belongs to a subnet not included on this switch, then
the packet should be sent to the next hop router (with the MAC address of the router itself used as
the destination MAC address, and the destination IP address of the destination node). The router
will then forward the packet to the destination node through the correct path. The router can also
use the ARP protocol to find out the MAC address of the destination node of the next router as
necessary.
NOTE
In order to perform IP switching, the switch should be recognized by other network nodes as an IP
router, either by setting it as the default gateway or by redirection from another router via the ICMP
process.
When the switch receives an IP packet addressed to its own MAC address, the packet follows the
Layer 3 routing process. The destination IP address is checked against the Layer 3 address table. If
the address is not already there, the switch broadcasts an ARP packet to all the ports on the
destination VLAN to find out the destination MAC address. After the MAC address is discovered, the
packet is reformatted and sent out to the destination. The reformat process includes decreasing
the Time-To-Live (TTL) field of the IP header, recalculating the IP header checksum, and replacing
the destination MAC address with either the MAC address of the destination node or that of the
next hop router.
When another packet destined to the same node arrives, the destination MAC can be retrieved
directly from the Layer 3 address table; the packet is then reformatted and sent out the destination
port. IP switching can be done at wire-speed when the destination address entry is already in the
Layer 3 address table.
If the switch determines that a frame must be routed, the route is calculated only during setup.
Once the route has been determined, all packets in the current flow are simply switched or
forwarded across the chosen path. This takes advantage of the high throughput and low latency of
switching by enabling the traffic to bypass the routing engine once the path calculation has been
performed.
Configuring IP Routing Interfaces
Configuring Local and Remote Interfaces
Use the IP > General > Routing Interface page to configure routing interfaces for directly connected
IPv4 subnets (see
“Setting the Switch’s IP Address (IP Version 4)” on page 1013.
If this router is directly connected to end node devices (or connected to end nodes through shared
media) that will be assigned to a specific subnet, then you must create a router interface for each
VLAN that will support routing. The router interface consists of an IP address and subnet mask.
This interface address defines both the network prefix number to which the router interface is
attached and the router’s host number on that network. In other words, a router interface address
defines the network segment that is connected to that interface, and allows you to send IP packets
to or from the router.
You can specify the IP subnets connected directly to this router by manually assigning an
IP address to each VLAN or using BOOTP or DHCP to dynamically assign an address. To specify IP
subnets not directly connected to this router, you can configure static routes (see
page 1044 ).