Showing posts from June, 2020

To Trunk or Not To Trunk, That Is the Question

Separate ISLs .  Trunked ISLs I have had several conversations recently with customers who have asked the question that when they have multiple inter-switch links (ISLs) between switches should those links be aggregated into a single logical link.  Above we have the two possible configurations for links between switches. On a Broadcom switch these are called trunks. On a Cisco switch these are called port-channels.   The word 'trunk' has a different meaning on a Cisco switch.  For Cisco, an inter-switch link (ISL)  is trunking when it is carrying traffic for multiple VSANs.  This applies to both single link ISLs and to port-channels.  If it is only carrying traffic for a single VSAN it is not trunking.  This blog post uses 'trunk' to mean link aggregation.  The first image above depicts three ISLs configured as separate, standalone ISLs.  The second image depicts the three links aggregated as a single logical link.  When link aggregation is configured,