How to influence EIGRP metrics to affect route selection

EIGRP updates contain five metrics: minimum bandwidth, delay, load, reliability, and maximum transmission unit (MTU). Of these five metrics, by default, only minimum bandwidth and delay are used to compute best path. Unlike most metrics, minimum bandwidth is set to the minimum bandwidth of the entire path, and it does not reflect how many hops or low bandwidth links are in the path. Delay is a cumulative value which increases by the delay value of each segment in the path.

Therefore we can change delay on interface to affect route selection, but this method can only be used when need to influence route selection learned via EIGRP neighbor on that interface.

Another more sophisticated way is to use offset-list, the metric of the route on the router can be modified using an offset-list on the neighbor router. Offset-list will insert the value to affect RD and FD advertised towards the peer router.


IPv6 address types


::1/128 loopback address, like in IPv4

FC00::/7 unique local address, like, 172,.16.0.0/12,

FF00::/8 multicast address, like

2000::/3 global unicast

2002::/16 used for 6to4 tunneling

2001:db8:cafe::/48 network specific prefix, used for nat64, IPv4/IPv6 address translation


EUI48 vs EUI64

refer to answer here:

Historically, both EUI-48 and MAC-48 were concatenations of a 24-bit OUI (Organizationally Unique Identifier) assigned by the IEEE and a 24-bit extension identifier assigned by the organization with that OUI assignment (NIC). The subtle difference between EUI-48 and MAC-48 was not well understood; as a result, the term MAC-48 is now obsolete and the term EUI-48 is used for both (but the terms “MAC” and “MAC address” are still used).

In other words, EUI-48 and the MAC number of a device represent the same thing! Usually it is represented in 12 hex (e.g. 0023.a34e.abc9), equivalent to 48 bits or 6 bytes.

By implementing the EUI-64 (64-bit Extended Unique Identifier format), a host can automatically assign itself a unique 64-bit IPv6 interface identifier without the need for manual configuration or DHCP. So it’s an IPv6 matter. Anyway, if you are interested about how it’s calculated, it is applied to a MAC address like this:

The 48-bit MAC address is split in half, the hex group FFFE is inserted in the middle (after the 24th bit), and the seventh bit is inverted.


The MAC address    0021.86b5.6e10      (48 bit) becomes 
the EUI-64 address 0221.86ff.feb5.6e10 (64 bit)


1, DIS is selected based on the highest priority, especially, DIS will be reselected whenever a new router is added into the lan segment. No backup DIS

2,to enable IS-IS on a Junos device, one of the parameters is the network entity title(NET), which is usually set on the lo0 interface, the NET contains the area ID, system ID and selector.

3,IS-IS adjacencies can only form when the level is the same for both peers, and for level 1, the neighbor must be in the same area

4, Link-state PDUs are sent as a response to a link-state request with a PSNP and during the formation of an IS-IS neighbor relationship. They are also sent as a triggered event when network changes occur.


RIP v2 in nutshell

1, RIP does not form adjacency for each other,  nor do they use hello protocol. It just send out update to the mulitcast destination ip with UDP protocol port 520. RIPv2 router can also configured to use the broadcast ip address, but this is not commonly done.

RIP can also send unicast update, when “neighbor ip-address” command is configured, identifys a neighbor to which unicast RIP updates will be sent.

RIPv2 has only 2 types of messages: requests and Responses

Update interval is 30 seconds by default, update will be full update, when routes change, update will be triggered as well.

2, RIPv2 convergence and loop prevention is realized by the following functions:

  • Counting to Infinity(16)
  • Split Horizon(should not be enabled in point-to-mulitpoint segment)
  • Route Poisoning
  • Split Horizon with Poisoned Reverse
  • Triggered update
  • Update time (30 secs by default)
  • Invalid after time (180 secs by default)
  • Holddown timer (180 secs by default)
  • Flushed after timer (240 secs by default)

When a router has one interface shutdown, router will flush the poisoned routes to all of other interfaces, the update will been sent immediately. When a router has a link down, after “Invalid after time”, the route will be set as invalid, holddown timer starts, after 60 secs, route will be flushed and holddown timer reset, the route change will trigger update as in the first scenario.

3, Routes can be filtered in both “in” and “out” direction by using distribute-list

4, RIPng for IPv6

5, “clear ip route *” command will clear the routing table entry and with RIP, sends RIP requests, quickly rebuilding the routing table

6, RIP version 2 support classless routes ads, but in order to advertise classless route, command “no auto summary” need to be configured.

IS-IS in nutshell

1, IS-IS is using NASP address to build up adjacency between each node, not IP address.

2, IS-IS is used to solve L1 and L2 routing problem described in

Especially L1 is similar with OSPF Not So Stub Totally Stub area, L1 area has no information about l2 routing and any other l2 area’s routing, it has only a default router (L1L2 router) which will connect this L1 area to L2 area; L2 area is similar with OSPF backbone area, which has information of both L2 and L1 areas.

When OSI network model is used, L2 will carry only area id info because L2 only need to forward the traffic towards correct L1 area, it does not have to know all ES address in L1 area. When IP is used, L2 will have IP information for networks directly connected in L2 router, and also the networks routes learned from L1 route calculation.

L1L2 router will have two IS-IS link databases, one is for L1 area which it connects to, the other is for L2. L1 and L2 databases are separated and can not be shared with each other, but L1L2 router will advertise routes learned according to L1 calculation to L2 database.

3, In IS-IS there are two types of network link: point-to-point and broadcast link. While point-to-multipoint can be simulated as several point-to-point links.

All interfaces in broadcast link will participate in DIS selection, like DR and BDR selection in OSPF broadcast link, but unlike DR and BDR role in OSPF, DIS in IS-IS is not the only one router which can send out LSP update, instead, all routers in  IS-IS broadcast link can send out LSP update. DIS is used to:

  • Help routers on a broadcast segment to synchronize
  • Representing the broadcast segment in the link-state database as a standalone object- The Pseudonode

4, Unlike OSPF which has several types of LSA, in IS-IS each router generate only one LSP, which includes all routes information of the router, LSP can be very long and need to be segmented to transfer in Layer two network, a sequence number will be used to identify the LSP packet sent by each router.  Router selected as DIS will generate 2 LSP: One is the general LSP for routing information, the other is Pseudonode LSP to indicate broadcast segment information. LSPID will be system ID + Pseudonode ID(local circuit ID of the interface)

5,  IS-IS has 3 adjacency states:

  • Down: the initial state
  • Initializing: IIHs have been received from the neighbout, but it is not certain that the neighbor is properly receiving this routers IIH
  • Up: IIHs have been received and also it is certain that the neighbor is properly receiving this router’s IIHs

6, IS-IS is a true multiprotocol routing protocol in the sense that it does not require any particular Layer 3 routing to carry it packets, and in a single instance, it can carry informaton of destination described by different address families, for example IPv4 and Ipv6 can be carried at the same time a single LSP and maintained in the same link state datebase.

OSI network & TCP/IP

OSI teminology: ES (end system)  is used as host in TCP/IP, IS( Intermediate System) is used for a router

In network layer of OSI reference model, there are 2 modes for end-to-end communication: connectionless-mode and connection mode. For connection-oriented mode, an adaptation of the x.25 is used, there is no analogous connection-oriented network layer protocol in TCP/IP. Connectionless-mode network protocol (clns) is to OSI networks what IPv4/v6 are to TCP/IP networks.

NSAP address is the address used in OSI reference model, unlike ip address, each IS node has only one NSAP address, each interface on the IS node is represented with local circuit ID. NSAP has minimum 8 octets, with only AFI, system ID and SEL. Tha maximum size is 20 octotets

Levels of Routing in OSI networks:

Level 0 routing: between ES and IS

Level 1 routing: between ES nodes within the same area

Level 2 routing: between ES nodes which are in the different area of the same domain

Level 3 routing:between ES nodes which are in different domains

IS-IS provice level 1 and level 2 routing. BGP  for inter-autonomous system routing in TCP/IP is fairly analogy of Level 3 routing.