Brocade BigIron RX Series Configuration Guide - Manual (Page 234)

156 BigIron RX Series Configuration Guide
53-1002484-04
The IP packet flow
7
FIGURE 5 IP Packet flow through a device
Figure 5 Shows the following packet flow:
1. When the device receives an IP packet, the device checks for IP ACL filters on the receiving
interface. If a deny filter on the interface denies the packet, the device discards the packet and
performs no further processing. If logging is enabled for the filter, then the device generates a
Syslog entry and SNMP trap message.
2. If the packet is not denied, the device checks for Policy Based Routing (PBR). If the packet
matches a PBR policy applied on the incoming port, the PBR processing is performed and
either drops the packet or forwards it to a port, based on the route map rules.
3. If the incoming packet does not match PBR rules, the device looks in the hardware IP routing
table to perform IP routing. The hardware routing table is pre-loaded with the complete routing
table, except for the directly connected host entries. Default and statically defined routes are
also pre-loaded in the hardware routing table. If the incoming packet matches a route entry,
the packet is routed according to the information provided in the route entry. The ECMP and
trunk load balancing is done by the hardware, if needed, to select the outgoing port.
4. If there is no match in the IP routing table and a default route is not configured, the packet is
dropped. For an IP packet whose destination IP address is to a directly connected host, the first
packet is forwarded to the CPU. If the ARP is resolved and the host is reachable, the CPU
creates a route entry in the hardware to route subsequent packets in hardware.
The software enables you to display the ARP cache and static ARP table, the IP route table, the IP
forwarding cache.
Incoming
Port
Drop
Permit
Deny IP ACLs
(hardware)
PBR
(hardware) Yes
No Next Hop
Table
(hardware)
Match
No Match IP Routing
(hardware) Forward to CPU
Lowest
Metric
Directly
connected
host
forwarding
cache
(software)
ECMP and
Trunk Load
Balancing
(hardware)
Outgoing
Port
IP Route
Table
(software)
ARP
Table
(software)
Static ARP
Table
Lowest
Admin.
Distance
RIP
OSPF
BGP4