Explanation/Reference:
Section: Enterprise Network Design Explanation
Explanation:
Port Aggregation Protocol (PAgP) is a Cisco-proprietary link-bundling protocol. Configuring multiple physical ports into a bundle, which is also known as a port group or an EtherChannel group, enables a switch to use the multiple physical ports as a single connection between a switch and another device.
Because bundled links function as a single logical port, Spanning Tree Protocol (STP) is automatically disabled on the physical ports in the bundle? however, spanning tree must be running on the associated port channel virtual interface to prevent bridging loops.
Typically, a link bundle is configured for high-bandwidth transmissions between switches and servers.
When a link bundle is configured, traffic is load balanced across all links in the port group, which provides fault tolerance. If a link in the port group goes down, that link's traffic load is redistributed across the remaining links.
PAgP cannot be used to create an EtherChannel on non-Cisco switches. In addition, PAgP cannot be used to create an EtherChannel link between a Cisco switch and a non-Cisco switch, because the EtherChannel protocol must match on each side of the EtherChannel link.
Link Aggregation Control Protocol (LACP) is a link-bundling protocol that is defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.3ad standard, not by Cisco. Because LACP is a standards-based protocol, it can be used between Cisco and non-Cisco switches.
Both PAgP and LACP work by dynamically grouping physical interfaces into a single logical link. However, LACP is newer than PAgP and offers somewhat different functionality. Like PAgP, LACP identifies neighboring ports and their group capabilities? however, LACP goes further by assigning roles to the link bundle's endpoints. LACP enables a switch to determine which ports are actively participating in the bundle at any given time and to make operational decisions based on those determinations.
Neither Hot Standby Router Protocol (HSRP) nor Virtual Router Redundancy Protocol (VRRP) is a link- bundling protocol. HSRP is a Cisco-proprietary first-hop redundancy protocol (FHRP). VRRP is an Internet Engineering Task Force (IETF)standard FHRP. Both HSRP and VRRP can be used to configure failover in case a primary default gateway goes down.
Reference:
Cisco: IEEE 802.3ad Link Bundling: Benefits of IEEE 802.3ad Link Bundling