Network Study Site

BGP Route Injection

2022 July 12

BGP Route Injection BGP route injection installs into the local routing table component prefixes of a summary route received via BGP. These more specific component prefixes are then advertised to BGP peers. BGP route injection is a method to deaggregate a BGP aggregate route ...

BGP Advertise-Map

2022 July 9

BGP Advertise-Map BGP conditional advertisement is a mechanism to influence inbound routing decisions. It is useful in dual homed scenarios where a router advertises its local prefixes to multiple BGP neighbors. Note that a BGP advertisement by a local router will attract traffic for that prefix. In response ...

DMVPN with OSPF

2022 June 30

DMVPN with OSPF DMVPN can be configured with the dynamic routing protocol OSPF. The different DMVPN Phases require specific adjustments when configuring OSPF. It is important to map multicast packets on the Hub and Spoke routers because OSPF Hellos rely on a multicast address to form neighborships ...

DMVPN Introduction

2022 June 29

DMVPN Introduction DMVPN Phases paired with different routing protocols provide solutions suited for a variety of use cases. DMVPN Phase 1 requires all traffic originating from spoke routers to travel through the hub router. In contrast, DMVPN Phase 2 and DMVPN Phase 3 enable direct spoke-to-spoke communication ...

Time-Based ACL

2022 June 28

Time-Based ACL A time-based access-list is only active during a specific time, either in a single point in time, or periodically repeating itself at a specific interval. The time-range command is used to configure an absolute or periodic time range during which an access-list will be active. An absolute time-range occurs ...

DMVPN NHRP Redirect

2022 June 27

DMVPN NHRP Redirect In DMVPN Phase 2 and Phase 3 there is direct spoke-to-spoke communication through a dynamically built GRE tunnel. This is achieved with the NHRP packet exchange between the DMVPN Spoke and Hub routers. In DMVPN Phase 3 specifically, the NHRP Redirect feature is used to build such a dynamic tunnel ...

ICMP Redirect with HSRP

2022 Jun 26

ICMP Redirect with HSRP An ICMP redirect enables a router to inform hosts about a preferred next-hop to their destination. An ICMP redirect message may be triggered if a router receives a packet and finds that the destination IP address can be reached by sending the packet out the same interface it was received on ...

BGP Dynamic Neighbor

2022 June 25

BGP Dynamic Neighbor The BGP dynamic neighbor feature reduces the administrative overhead on routers that receive frequent BGP peering requests. By configuring dynamic neighbors, a local router automatically establishes BGP neighborships if a remote router falls within a configured "listen range" ...

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