IEEE 802.1Q/MAC Addresses in Router 2800 Series

Unanswered Question
Oct 30th, 2009

Dear Sir/Madam,

I would like to find the number of VLANs I may configure in a Router 2800 Series and the maximum number of MAC Addresses.

Kind Regards

I have this problem too.
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imavrogianni Fri, 10/30/2009 - 06:19

I want to find a document (.pdf)regarding the number of VLANs and the MAC Addresses because it is in the framework of a tender and I must comply to the Table of Compliance.

Paolo Bevilacqua Fri, 10/30/2009 - 07:59

No such document exist, router has no maximum macs and I've indicated you already max vlans is 4095.

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Peter Paluch Fri, 10/30/2009 - 06:16

Hello Ismini,

The number of concurrent VLANs supported on a router is limited by several factors.

A router consumes one subinterface for each supported routed VLAN on a physical interface. Each subinterface is described internally in IOS using a software interface descriptor block, or IDB. There is an upper limit on the number of IDBs existing on a router, and therefore, an upper limit on total number of subinterfaces with distinct VLANs. This limit is platform and IOS version dependent, however, as an example, on an 2801 router running 12.4(4)XC2 Advanced IP Services IOS, the maximum IDB count is 1200. This limit can be always verified using the show idb command. Note that it does not matter here whether there are 1200 subinterfaces under a single physical interface, or two physical interfaces having 600 subinterfaces each.

These are routed VLANs - those that are created as subinterfaces on routed physical ports. If, however, you are asking about the number of VLANs supported for an additional switching module such as HWIC-4ESW, this limit is much lower. On the same router, the limit is 16 and I personally suspect that it is the limitation of the HWIC module, not of the IOS itself.

Best regards,

Peter

Peter Paluch Fri, 10/30/2009 - 14:33

Hello Ismini,

I am honestly unaware of a PDF file regarding the maximum number of IDS for the IOS and platform you are looking for. But if in serious need, you may take the number 1200 as the limit in the 12.4 IOS for 2801 series routers. Perhaps other colleagues here having other 2800 platforms and IOSes could share their show idb results with you.

Regarding the maximum MAC addresses, what exactly are you interested in? These routers do not have a MAC address table as switches do so in this aspect, it is not possible to answer. If you are asking about the size of an ARP cache, then there is no prescribed limit as far as I know - the ARP cache is only limited by the available DRAM on a router. The 802.1Q subinterfaces on routed ports do not require additional MAC addresses. Also, the VLAN SVI interfaces created for switching modules share the same MAC address, so the MAC address limit in this respect should not be of a concern.

Best regards,

Peter

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