Routing

Question 1

is ECMP enabled by default?

Answer 1

NO!

Question 2

what are the primary v4 and v6 routing tables?

Answer 2

inet.0 – v4 unicast
inet.1 – multicast forward cache
inet.2 – Multicast BGP (MBGP) for RPF checks
inet.3 – for MPLS path info
inet.4 – for Multicast source discovery routes
inet6.0 – v6 unicast
mpls.0 – mpls nexthops

Question 3

Whats AD in Junos?

Answer 3

Route preference

Question 4

What are the preferences for:

BGP, RIP, OSPF Internal, Direct, Static, Local, OSPF External?

Answer 4

Direct = 0
Local = 0
Static = 5
OSPF internal = 10
RIP = 100
OSPF AS External = 150
BGP = 170

Question 5

Route preference… High or low preferred?

What’s the range?

Answer 5

low is best. 4.2 billion is highest (32bit int)

Question 6

how do you see all routes for a given prefix in the RIB?

Answer 6

show route <prefix> exact</prefix>

Question 7

Can you change route preference?

Answer 7

yes, but local and direct dont actually have any impact if you change em.

Question 8

Default behaviour - how does ECMP work?

Answer 8

if there are two Equal cost routes to the same prefix, one path is picked at random.

This means where lots of prefixes are going across an equal cost link there is load distribution.

You can turn on per-flow ECMP.

Question 9

how do you see route tables?

Answer 9

show route.

Question 10

how do you see forwarding table?

Answer 10

show route forwarding-table

Question 11

what happens if there is no match in the forwarding table?

Answer 11

packet hits the default FIB entry.

Question 12

what are the two types in the FIB?

Answer 12

1st = Route type… dest (Destinations reachable), intf (local interfaces), perm (kernel installed things like multicast addresses, broadcast addresses), User (routes installed by a routing protocol or static config)

2nd = next hop type - broadcast, discard (silent), hold (pending resolution), local, multicast, multicast discard, recieve, reject, unicist, and load ballanced unicast.

Question 13

In FIB, whats difference between DISCARD and REJECT?

Answer 13

DISCARD = drop quiet
REJECT = ICMP unreachable is sent

Question 14

Whats a routing instance?

Answer 14

its basically VRF lite

Question 15

Whats the default routing instance?

Answer 15

Master.

Question 16

How do you set configure a routing instance type on a custom routing instance?

Answer 16

edit routing-instances <instance>
set instance-type</instance>

Question 17

what are the routing instance types?

Answer 17

forwarding - for FBF for normal access layer applications

l2vpn - for l2vpn…
no-forwarding - used to split up huge networks
virtual-router - for non-VPN related application like virtualization
vpls - for point to multipoint VPN
vrf - for layer3 VPN

Question 18

How do you create a routing instance?

Answer 18

edit routing-instance <name>
set instance-type <type>
set interface <interface>
set interface <interface>
set interface <interface>
set routing-options static route 0.0.0.0/0 next-hop x.x.x.x
set protocols ospf area 0.0.0.0 interface ge0/x/x
set protocols ospf area 0.0.0.0 interface ge0/y/y</interface></interface></interface></type></name>

Question 19

where do you configure interfaces and routing protocols for routing instances?

Answer 19

inside the routing instance itself

Question 20

how do you view routing instance tables?

Answer 20

show route table <routing>.routingtable</routing>

eg;

show route table vrf1.inet.0

Question 21

how do you see interfaces in a given routing instance?

Answer 21

show interfaces terse routing-instance <name></name>

Question 22

where do you configure a static route?

Answer 22

from edit routing-options!

Question 23

what’s the equlivent of null0 for Junos?

Answer 23

bitbucket

Question 24

whats the deal with static route next hops on junos?

Answer 24

static route next hops must by default be a connected interface.

No recursive lookups unless you enable it.

Question 25

how long are static routes in the rib?

Answer 25

until they are removed or go inactive (ie, next-hop is unreachable, interface down or w/e)

Question 26

what are default static routes for v4 and v6?

Answer 26

edit routing-options rib inet6.0
set static route 0::/0 next-hop 3001::1
edit routing-options
set static route 0.0.0.0/0 next-hop x.x.x.x.x
set static route x.x.x.x/24 next-hop y.y.y.y.y no-readvertise

Question 27

when should no-readvertise be used?

Answer 27

management static routes. blocks redistribution.

Question 28

how do you see static routes in the rib?

Answer 28

show route protocol static

Question 29

how do you add recursive lookups on static routes?

Answer 29

add the resolve keyword on the static route.

If the resolved next-hop drops the route goes down.

Question 30

whats a qualified next hop?

Answer 30

its a backup next-hop. You can even set a floating preference.

Question 31

What do you need to do to turn on ipv6?

Answer 31

its on platform wide by default, but you have to add the inet6 address family to the interface

this configures a link local

Question 32

how do you configure an ipv6?

Answer 32

same as v4, just inet6 not inet…

edit interface <int> unit 0
set family inet6 address <address></int>

Question 33

how do you enable EUI-64?

Answer 33

on the interface unit;

set family inet6 address <subnet>/64 eui-64</subnet>

and it’ll hash you an IP from the MAC

Question 34

whats the OSPF for IPv6?

Answer 34

RFC5340.

Basically the same; just use ospf3 instead of ospf on the interface to add it to the v6 compatible OSPF process.