Wednesday, July 30, 2014

What is Packet Ricochet?

We will discuss about Packet Ricochet in Rivervbed SteelHead. Packet ricochet is a condition where the Steelhead sees the same data more than once. Simplified routing option in Riverbed SteelHead avoids situations when a packet traverses a SteelHead more than once.

The packet ricochet scenarios only occur in physically in-path environments where the SteelHead is installed in a subnet different than the clients or servers. In these environments, you can avoid packet ricochet by either configuring static routes or by using simplified routing.

  • Some environments that include firewalls or routers with ACLs might not permit traffic to ricochet, or traverse back out the same interface as it came in.

  • Some monitoring tools that rely on NetFlow or SNMP data count the ricocheted traffic as additional traffic.

  • Packet ricochet causes the adjacent network devices to perform unnecessary work.

Figure 1.1: shows an example of packet ricochet when the SteelHead default gateway is configured for the WAN router, the host sits on a different network than the SteelHead, and simplified routing is not enabled.

Figure 1.2 shows a similar packet ricochet scenario, but with the default gateway of the SteelHead pointed to the LAN L3 switch.

You can configure a static route for the host network, to point directly to the L3 switch, preventing this traffic from using the default gateway. However, the static route method often becomes administratively burdensome, especially in larger or complex LAN environments.

Simplified routing resolves packet ricochet, without using static routes or routing protocols, by building an IP to next-hop MAC address mapping learned from received packets. The SteelHead learns the correct MAC address by examining the packet's destination or source IP and MAC address.

Only use simplified routing for optimized traffic generated by the SteelHead, For pass-through traffic, the SteelHead sends the packets out the opposite WAN or LAN interface as it came in. You can also use simplified routing when the destination IP is on a different subnet than the SteelHead in-path IP. If the destination IP resides on the same network, the SteelHead uses ARP for the correct MAC address. When the destination IP resides on a different network, then a simplified routing entry (if recorded) takes precedence over the default gateway, or by default, any configured static routes.

To override the default behavior and have the static routes take precedence over simplified routing, use the following CLI command:

in-path simplified mac-def-gw-only

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1 comment:

  1. Very Good Article, It helped me understand simplified routing in riverbed, Thanks a lot!!!