What are the link aggregation protocols in Cisco Switches, what are their modes required to bundle a link?

Dynamic Configuration Cisco switches support two dynamic aggregation protocols: PAgP (Port Aggregation Protocol) – Cisco proprietary aggregating protocol. LACP (Link Aggregation Control Protocol) – IEEE standardized aggregation protocol, originally defined in 802.3ad. PAgP and LACP are not compatible – both sides of an Etherchannel must use the same aggregation protocol. EthernChannel – PAgP It supports [...]

In Cisco Switches for VTP, what frame tagging protocol they support?

Cisco switches support two frame tagging protocols: Inter-Switch Link (ISL) IEEE 802.1Q Inter-Switch Link (ISL) It is Cisco’s proprietary frame tagging protocol.  It encapsulates a frame with an additional header (26 bytes) and trailer (4bytes). It increases the size of a frame by 30 bytes. The header contains several fields, including a 15-bit VLAN ID. [...]

What is Multi VLAN port ?

The multi-VLAN port is a feature which allows switch for configuring a single port for two or more vlans. This feature allows users from different VLANs to access a server or router without implementing InterVLAN routing capability. A multi-VLAN port performs normal switching functions in all its assigned VLANs. Multi-VLAN port will not work when [...]

What is error disable state? How to recover from error disable port?

The ErrDisable feature is implemented to handle critical situations where the switch detected excessive or late collisions on a port, port duplex misconfiguration, Ether Channel misconfiguration, Bridge Protocol Data Unit (BPDU) port-guard violation, UniDirectional Link Detection (UDLD), and other causes. The error-disable function let the switch to shut down a port when it encounters physical, [...]

How to configure the Sup engine redundancy in the Cisco 6500?

To set up the SUP engine redundancy one must have the same version of iOS. Once Sup engine redundancy is configured one switch will act as Active Sup and the other will act as standby sup engine Cisco6500(config)# redundancy Cisco6500(config-red)#keepalive-enable Cisco6500(config-red)#mode sso Cisco6500(config-red)#main-cpu Cisco6500(config-red-main-cpu)#auto-sync running-config SSO (Stateful Switch over) mode means it will sync the [...]

What is BPDU

BPDU’s are the messages exchanged between switches to calculate the spanning tree topology.Bridge Protocol Data Units (BPDU’s) frames contain information regarding the Switch ID, originating switch port, MAC address, switch port priority, switch port cost etc. Bridge Protocol Data Units (BPDU’s) frames are sent out as multicast messages regularly at multicast destination MAC address 01:80:c2:00:00:00. [...]

What will happen if two switch are connected to each other by two cables and spanning tree is disabled?

When a redundant connection is made, we will start receiving MAC address flapping notifications such as %SW_MATM-4-MACFLAP_NOTIF: Host 003b.20c2.0264 in vlan 1 is flapping between port Fa0/4 and port Fa0/5 These are triggered by the never-ending broadcast storm initiated by every layer two broadcast (such as an ARP request) from any host on the VLAN. [...]

What does the Spanning tree algorithem do? What are the modes that it can be in?

The STP algorithm is responsible for identifying active redundant links in the network and blocking one of these links, thus preventing possible network loops. There are four modes of Spanning tree -PVST+ -RSTP -Rapid-PVST+ -MSTP Cisco Proprietary Per-VLAN Spanning Tree Protocol (PVST) – Maintains a spanning-tree instance for each VLAN configured in the network. It [...]