Dell BigIron RX Series, Руководство по настройке

Страница: 230 / 1458

154 BigIron RX Series Configuration Guide
53-1002253-01
The IP packet flow
7
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.
ARP cache table
The Address Resolution Protocol (ARP) is supported on the device. Refer to “IP fragmentation
protection” on page 185.
The ARP cache contains entries that map IP addresses to MAC addresses. Generally, the entries
are for devices that are directly attached to the device or virtual interfaces.
An exception is an ARP entry for an interface-based static IP route that goes to a destination that is
one or more router hops away. For this type of entry, the MAC address is either the destination
device’s MAC address or the MAC address of the router interface that answered an ARP request on
behalf of the device, using proxy ARP.
The ARP cache can contain dynamic (learned) entries and static (user-configured) entries. The
software places a dynamic entry in the ARP cache when the device learns a device’s MAC address
from an ARP request or ARP reply from the device.
The software can learn an entry when the device receives an ARP request from another IP
forwarding device or an ARP reply. Here is an example of a dynamic entry.
Each entry contains the destination device’s IP address and MAC address.
Static ARP table
In addition to the ARP cache, the device has a static ARP table.
Entries in the static ARP table are user-configured. You can add entries to the static ARP table
regardless of whether the device the entry is for is connected to the device.
IP Address MAC Address Type Age Port
1 207.95.6.102 0800.5afc.ea21 Dynamic 0 6