Tejas Jain

The AD values of the protocols are generally different across different vendors and care must be taken to take this fact into account in case of multi-vendor environments. Cisco Directly Connected Interface = 0 Static route = 1 EIGRP summary route = 5 External Border Gateway Protocol (eBGP) = 20 Enhanced Interior Gateway Routing Protocol (EIGRP) - Internal = 90 Open Shortest Path First (OSPF) = 110 Intermediate System to Intermediate System = 115 Routing Information Protocol (RIP) = 120 Enhanced Interior Gateway Routing Protocol (EIGRP) - External = 170 Internal Border Gateway Protocol (iBGP) = 200 Juniper Directly Connected Interface = 0 Static route = 5 Intermediate System to Intermediate System - Level-1 Internal = 15 Intermediate System to Intermediate System - Level-2 Internal = 18 Routing Information Protocol (RIP) = 100 Summary Route (Aggregate route) = 130 Open Shortest Path First (OSPF) = 150 Intermediate System to Intermediate System - Level-1 External = 160 Intermediate Syst...

Most routing protocols have metric structure that are not comparable with each other, in case multiple protocols are being used in a network. For eg. RIP uses hop count and OSPF uses cost for best path selection to a particular route. In order to have a common parameter which can be used for computing the best path, the concept of Administrative Distance (AD) was introduced. AD is simply a number which helps identity a particular route learned from a particular protocol. For eg, if the route is learned from Routing Information Protocol (RIP), then it would have a default AD value of 120 (unless it has been explicitly modified). Similary, a route learned from OSPF would have the AD value of 110. Rule: A route with lower Administrative Distance (AD) value would always be preferred over the one with higher AD value. In the above scenario, if the route is being learned from both RIP as well as OSPF, then the route learned via OSPF would be preferred since OSPF has a lower AD value of 110 t...

Cisco Software Defined Access is a new paradigm towards building Enterprise Networks. Primarily built upon the Cisco's DNA Center software, it leverages several next-generation components to design, provision and apply policy to create an intelligent wired and wireless network infrastructure. Cisco DNA Assurance which turns the network devices into sensors, giving visibility to everything on the network; guided remediation which automates resolution to keep the network at its optimal performance and thereby improve the end user experience, are some of Cisco's USPs. Cisco SDA accomplishes this intent based networking via the following components: Fabric Control Plane nodes: Based on LISP map-server and map-resolver functionality combined together on the same node, control plane node (database) tracks the endpoints in the fabric site and associates the endpoints to fabric nodes. Border nodes and edge nodes register with the control plane nodes. Control Plane node can be dedicate...

One of the most intriguing (of course, if you get the hang of it) or depressing concepts of Cisco ACI is how the traffic forwarding takes place inside Cisco ACI. Let's start with an endpoint sending the frame to the connected leaf: The leaf checks the destination MAC address of the frame. The leaf will do a layer 2 lookup to find the destination MAC. If the leaf knows the location of the destination MAC (either local to the leaf or some other leaf), it will determine the destination's EPG. Depending on the EPG, it would determine if a contract is required to allow the frame to forward.. If yes, it would look into the L3 and L4 contents of the packet to determine if the contract exists. If it does, allow the traffic, if not drop. If the frame has the destination MAC address of that of the leaf, it will be routed. This will be the standard destination IP based routing. If a route exists for the destination in the VRF of the source, it is routed. If not, it will be dropped. With r...

Unlike the traditional Cisco switching world, where there existed only 3 VLAN types (standard, extended, private), Cisco ACI is definitely supposed to have several of them, to ensure that multitudes of Network Professionals get their brains wired! Luckily, I came across the following ones which seem to make sense about their respective roles to have the traffic forwarding in place: VLAN ID ( VlanID ) - Platform independent VLAN that is locally significant to each switch. This VLAN is automatically bound to the port-group VLAN existing on the DVS. It is derived from the VLAN pool that is configured in the Fabric Access Policies. Hardware VLAN ID ( HW_VlanId ) - In order to switch traffic locally, most leaf switches comprise of Broadcom ASIC. This VLAN type is utilized by the Broadcom ASIC chip. Connect to Broadcom ASIC on the leaf : vsh_lc To generate the list of endpoints connected : show system internal eltmc info vlan brief The various VLAN types are: BD_CTRL_VLAN - Infrastructure...

What is a switch fabric module? Fabric module connects the supervisor engine and line cards of the switch Fabric Module Types Fabric Module - 1 - Generation 1 (provides 46 Gbps of backplane capacity) Fabric Module - 2 - Generation 2 (provides 110 Gbps of backplane capacity) Fabric Module - 3 - Generation 3 (provides 2.8 Tbps of backplane capacity) What do the above numbers indicate? The original M1 series I/O modules eg. N7K-M132XP-12 have 80 Gbps of capacity per slot. So, two Generation 1 fabric modules would be required (2*46Gbps = 92 Gbps) for providing sufficient fabric capacity for the M1 series 10GE line card. Ordinarily, Cisco would recommend using 3 fabric modules in this case, for redundancy purposes, since one fabric module going down would translate to reduced capacity / backplane in the production environment. This implies, the overall fabric module capacity should exceed the line card capacity. Hardware specific details Nexus 7004 has no fabric modules Nexus 7000 series su...

During the fabric registration process, an ACI node usually transitions across different states. These states are usually recorded in the Fabric Node Vector (FNV) table, which can be checked using the below command on the APIC acidiag fnvread States and descriptions: Unknown – Node has been discovered but no Node ID policy has been configured Undiscovered – Node ID has been configured but the node is yet to be discovered Discovering – Node has been discovered but VTEP IP has not yet been assigned Unsupported – Node is not a supported model Disabled – Node has been decommissioned Inactive – There is no IP connectivity Active – Node is active