Routing Flashcards
is ECMP enabled by default?
NO!
what are the primary v4 and v6 routing tables?
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
Whats AD in Junos?
Route preference
What are the preferences for:
BGP, RIP, OSPF Internal, Direct, Static, Local, OSPF External?
Direct = 0
Local = 0
Static = 5
OSPF internal = 10
RIP = 100
OSPF AS External = 150
BGP = 170
Route preference… High or low preferred?
What’s the range?
low is best. 4.2 billion is highest (32bit int)
how do you see all routes for a given prefix in the RIB?
show route <prefix> exact</prefix>
Can you change route preference?
yes, but local and direct dont actually have any impact if you change em.
Default behaviour - how does ECMP work?
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.
how do you see route tables?
show route.
how do you see forwarding table?
show route forwarding-table
what happens if there is no match in the forwarding table?
packet hits the default FIB entry.
what are the two types in the FIB?
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.
In FIB, whats difference between DISCARD and REJECT?
DISCARD = drop quiet
REJECT = ICMP unreachable is sent
Whats a routing instance?
its basically VRF lite
Whats the default routing instance?
Master.
How do you set configure a routing instance type on a custom routing instance?
edit routing-instances <instance>
set instance-type</instance>
what are the routing instance types?
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
How do you create a routing instance?
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>
where do you configure interfaces and routing protocols for routing instances?
inside the routing instance itself
how do you view routing instance tables?
show route table <routing>.routingtable</routing>
eg;
show route table vrf1.inet.0
how do you see interfaces in a given routing instance?
show interfaces terse routing-instance <name></name>
where do you configure a static route?
from edit routing-options!
what’s the equlivent of null0 for Junos?
bitbucket
whats the deal with static route next hops on junos?
static route next hops must by default be a connected interface.
No recursive lookups unless you enable it.
how long are static routes in the rib?
until they are removed or go inactive (ie, next-hop is unreachable, interface down or w/e)
what are default static routes for v4 and v6?
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
when should no-readvertise be used?
management static routes. blocks redistribution.
how do you see static routes in the rib?
show route protocol static
how do you add recursive lookups on static routes?
add the resolve keyword on the static route.
If the resolved next-hop drops the route goes down.
whats a qualified next hop?
its a backup next-hop. You can even set a floating preference.
What do you need to do to turn on ipv6?
its on platform wide by default, but you have to add the inet6 address family to the interface
this configures a link local
how do you configure an ipv6?
same as v4, just inet6 not inet…
edit interface <int> unit 0
set family inet6 address <address></int>
how do you enable EUI-64?
on the interface unit;
set family inet6 address <subnet>/64 eui-64</subnet>
and it’ll hash you an IP from the MAC
whats the OSPF for IPv6?
RFC5340.
Basically the same; just use ospf3 instead of ospf on the interface to add it to the v6 compatible OSPF process.
