WS-C5509 out-lost

Unanswered Question
Dec 17th, 2007

I have little problem with multicast traffic in our network. Lots of that kind of traffic is going and end users start to see it. Trunk ports have big traffic peak sometimes and every time when that peak is coming end users see it. In core WS-C5509 i can see after traffic peak lots of out-lost octets in those trunk links. (command sho mac mod/port) What that migt tell. Does the switch drop packets. Any idea


thanks

Juha

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smahbub Tue, 12/25/2007 - 06:38

Trunk ports enable connections between switches to carry traffic from more than one VLAN. If trunking is not enabled, the link that connects the two switches only carries traffic from the VLAN that you have configured on the port. Trunking is not necessary in very simple switched networks with only one VLAN (broadcast domain). In most LANs, a small portion of traffic consists of special protocols that manage the network. (A few examples are Cisco Discovery Protocol [CDP], VLAN Trunk Protocol [VTP], Dynamic Trunking Protocol [DTP], Spanning Tree Protocol [STP], and Port Aggregation Protocol [PAgP].) You also use the management VLAN when you ping or establish a Telnet directly to or from the switch. (If you use Catalyst OS [CatOS], you define the VLAN and the IP address of the switch when you configure the sc0 interface. The Step-by-Step Instructions for CatOS section of this document explains this process.) In a multi-VLAN environment, many network administrators advocate the restriction of this management traffic to a single VLAN. The VLAN is normally VLAN 1. The administrators then configure user traffic to flow in VLANs other than this default VLAN.


glen.grant Tue, 12/25/2007 - 10:58

If that trunk link is running near its capapcity at say 85-95% of say a 100 meg link we have seen where yes it will start to drop packets. If this is a problem then think about adding etherchannel for added capacity across those links. Also if you have multiple vlans and your not setup for multicasting this can put a heck of a load on switches . I have seen a single mutlicast user bury a 6509 sup 720. If this multicast is legitimate traffic that you want on your network then you should think about setting up your network for multicast routing if not you should track down those users and get that function turned off.

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