Intelligent Oversubscription on the Trio DPC and MPC/MIC Interfaces Overview

On the Trio DPC and MPC/MIC interfaces, as on other types of interface hardware, arriving packets are assigned to one of two preconfigured traffic classes (network control and best effort) based on their header types and destination media access control (MAC) address. Oversubscription, the situation when the incoming packet rate is much higher than the Packet Forwarding Engine and system can handle, can cause key packets to be dropped and result in a flurry of resends, making the problem worse. However, the Trio DPC and MPC/MIC interfaces handle oversubscription more intelligently and drops lower priority packets when oversubscription occurs. Protocols such as routing protocols are classified as network control. Protocols such as telnet, FTP, and SSH are classified as best effort. No configuration is necessary.

The following frames and packets are assigned to the network control traffic class:

• ARPs: Ethertype 0x0806 for ARP and 0x8035 for dynamic RARP
• IEEE 802.3ad Link Aggregation Control Protocol (LACP): Ethertype 0x8809 and 0x01 or 0x02 (subtype) in first data byte
• IEEE 802.1ah: Ethertype 0x8809 and subtype 0x03
• IEEE 802.1g: Destination MAC address 0x01–80–C2–00–00–02 with Logical Link Control (LLC) 0xAAAA03 and Ethertype 0x08902
• PVST: Destination MAC address 0x01–00–0C–CC–CC–CD with LLC 0xAAAA03 and Ethertype 0x010B
• xSTP: Destination MAC address 0x01–80–C2–00–00–00 with LLC 0x424203
• GVRP: Destination MAC address 0x01–80–C2–00–00–21 with LLC 0x424203
• GMRP: Destination MAC address 0x01–80–C2–00–00–20 with LLC 0x424203
• IEEE 802.1x: Destination MAC address 0x01–80–C2–00–00–03 with LLC 0x424203
• Any per-port my-mac destination MAC address
• Any configured global Integrated Bridging and Routing (IRB) my-mac destination MAC address

In addition, the following Layer 3 control protocols are assigned to the network control traffic class:

• IGMP query and report: Ethertype 0x0800 and carrying an IPv4 protocol or IPv6 next header field set to 2 (IGMP)
• IGMP DVMRP: IGMP field version = 1 and type = 3
• IPv4 ICMP: Ethertype 0x0800 and IPv4 protocols = 1 (ICMP)
• IPv6 ICMP: Ethertype 0x86DD and IPv6 next header field = 0x3A (ICMP)
• IPv4 or IPv6 OSPF: Ethertype 0x0800 and IPv4 protocol field or IPv6 next header field = 89 (OSPF)
• IPv4 or IPv6 VRRP: IPv4 Ethertype 0x0800 or IPv6 Ethertype 0x86DD and IPv4 protocol field or IPv6 next header field = 112 (IGMP)
• IPv4 or IPv6 RSVP: IPv4 Ethertype 0x0800 or IPv6 Ethertype 0x86DD and IPv4 protocol field or IPv6 next header field = 46 or 134
• IPv4 or IPv6 PIM: IPv4 Ethertype 0x0800 or IPv6 Ethertype 0x86DD and IPv4 protocol field or IPv6 next header field = 103
• IPv4 or IPv6 IS-IS: IPv4 Ethertype 0x0800 or IPv6 Ethertype 0x86DD and IPv4 protocol field or IPv6 next header field = 124
• IPv4 router alert: IPv4 Ethertype 0x0800 and IPv4 option field = 0x94 (router alert)

Also, the following Layer 4 control protocols are assigned to the network control traffic class:

• IPv4 and IPv6 BGP: IPv4 Ethertype 0x0800 or IPv6 Ethertype 0x86DD, TCP port = 179, and carrying an IPv4 protocol or IPv6 next header field set to 6 (TCP)
• IPv4 and IPv6 LDP: IPv4 Ethertype 0x0800 or IPv6 Ethertype 0x86DD, TCP or UDP port = 646, and carrying an IPv4 protocol or IPv6 next header field set to 6 (TCP) or 17 (UDP)
• IPv4 UDP/L2TP control frames: IPv4 Ethertype 0x0800, UDP port = 1701, and carrying an IPv4 protocol field set to 17 (UDP)
• DHCP: Ethertype 0x0800, IPv4 protocol field set to 17 (UDP), and UDP destination port = 0x43 (DHCP service) or 0x44 (DHCP host)
• IPv4 or IPv6 UDP/BFD: Ethertype 0x0800, UDP port = 3784, and IPv4 protocol field or IPv6 next header field set to 17 (UDP)

Finally, any PPP encapsulation (Ethertype 0x8863 (PPPoE Discovery) or 0x8864 (PPP0E Session Control)) is assigned to the network control traffic class (queue 3).

Note: These classifications are preconfigured.