2001:6F8:147F:42:88C1:76FF:FE44:6CCE: /* The 7-layer burrito */

2010-10-03T22:30:52Z

‎The 7-layer burrito

2001:6F8:147F:42:88C1:76FF:FE44:6CCE: /* The 7-layer burrito */

2010-10-03T22:29:19Z

‎The 7-layer burrito

2001:6F8:147F:42:88C1:76FF:FE44:6CCE: /* BGP */

2010-10-03T22:27:36Z

‎BGP

Jeroen De Dauw at 18:14, 3 October 2010

2010-10-03T18:14:23Z

Jeroen De Dauw: /* Talk notes */

2010-10-03T16:22:03Z

‎Talk notes

78.22.102.245: Created page with "= Talk notes = == The 7-layer burrito == layers let's say you get ethernet-frame in there vlan-tag in the payload can be another vlan tag payload can be ip-packet with in there..."

2010-10-03T16:21:11Z

Created page with "= Talk notes = == The 7-layer burrito == layers let's say you get ethernet-frame in there vlan-tag in the payload can be another vlan tag payload can be ip-packet with in there..."

New page

= Talk notes =

== The 7-layer burrito ==
layers

let's say you get ethernet-frame
in there vlan-tag
in the payload can be another vlan tag
payload can be ip-packet
with in there another ip-packet (like a tunnel)

=== 7 layers of crap ===

* 80's: OSI : idea of defining 7 layers with the idea that each use/protocol fits in exactly one of those layers
* more like a thought experiment
* today: things don't fit in these layers,really:

the only thing that fits the 7-layer model is the burrito: the tasty mexican snack,
* 7 layer burrito: http://pablotron.org/files/7_layer_burrito.html

== Why classful addressing will get you fired ==

=== What's an ip address?: you're all wrong ===

1.2.3.4 / mask
* it describes a host? nope: it describes an interface on a host
* the mask describes the size of the network it is directly connected to

if you want to make host listen to some ip-address, no routing over this ip then
bind interfaces to a _host, not to specific interface

so alias interfaces are plain wrong for this
eg. don't do eth:1 but do use lo:1
use your loopback interface to do this: packets coming in on any interface will be processed by kernel -- mask doesn't matter as we're not routing over these /32 is common

=== Class-C, and you're fired ===

Darpa developed it, ip protocol,
IANA chopped it to several classes: assignment on class of organisation.
Everyone wanted their own class c, ip's were filling up.
Solution:
http://en.wikipedia.org/wiki/Subnetwork

CIDR notation (_classless_ interdomain routing) 1.2.3.4/23

* what you'll find on the network-engineers' cheatsheet
bit mask nr of hosts
/23 255.255.254.0 512

first address in subnet always refers to subnet
last is broadcast address

* /30 4 addresses : 2 hosts + network + broadcast : link between two hosts
* /31 networks in theory it's useless, but cisco used it in specific case : network with two hosts, no broadcast/network

CIDR is put in RFC1519 (1993 - 17 years ago) B. kicks everybody in the n*ts if they talk about

routing
* rauting: US
* roeting: EU (mainly french influence)
use whatever pronunciation

== Routing is not forwarding ==

=== Forwarding ===

machine with different interfaces: takes input from one, decides where it should go (table lookup or something), forwards it to other interface.

forwarding table
* FIB (forwarding information base)
* switching fabric (in a switch)w

on a linux box
* 'cpu only forwarding' (packet comes in, stored in queue, wakes cpu, cpu puts it to queue of other interface) : slow, doesn't scale (lot's of memtransfer etc) - one packet-one interrupt
* NAPI: new-api: kernel switches of interrupt while processing queue
* juniper IP2: separate eth+ip header (first64byte eth header is 16 bytes ip is 20 bytes, other stuff might add to that, but it all fits easily in 64 bytes) from the payload - it contains all info needed for forwarding - the payload is mapped in memory(so not transferred, copied over in
* switching fabric
* matrix - bunch of interconnects

simpsons and computers http://www.snpp.com/guides/computers.file.html

but how do you know where to forward yr packet to ?
* switch looks at destination MAC (eth header contains src & dst mac)
* router looks at IP-header : destination IP
** destination based forwarding (aka forwarding)
** lookup type in ETH-header : check if it's IP, check DST IP

lookups in patricia-tree (aka radix-tree)
http://en.wikipedia.org/wiki/Radix_tree

** if you have to do this for _every packet, you're in quite a lookup-pain

solution: MPLS http://en.wikipedia.org/wiki/Multiprotocol_Label_Switching
tagging packets, so MPLS enabled routing infrastructure can forward the packet without repeated IP routing lookup
** the path this packet is following is called LSP: label switched path ==> unidirectional

there are quite some applications built upon bare MPLS (eg vpn setup on top of it )

how to configure your MPLS network?
LDP (label distribution protocol)- setup tunnels
RSVP (resource reservation protocol)

basic priority queue-ing -- traffic-class / forwarding classes
BE - best effort (aka the internet)
AF - assured forwarding
EF - expedited forwarding - blast it all out
An mpls tag contains what priority class should be used (probably, not entirely sure)
** you can map these to vlan-priority-tags

VRF - used for VPN (only), on start & end forwarding node
(having multiple independent routing tables on system - priority routing )

== Dynamic routing is not scary ==

forwarding: taking ip prefixes and deciding which interface to push them out to
routing: influences the forwarding
routing is not forwarding

how big is the network behind yr interface: the netmask

ip-addr :
* makes your computer listen to request for that address
* makes an entry in routing table

0.0.0.0/0 : yr good ol' trusty default route - real men got numpads

=== Static routing ===

* multiple routes to one host: router will probably roundrobin over both routes/ so when one goes down you get 50% (if you have two routes) packetloss... (and yr voip etc goes down)
* provide a lot of control, but when shit hits fan and routes go down, y're in trouble

=== Dynamic routing ===

* routing protocols: rip, ospf, isis, etc
* routers publish subnets connected to their interfaces
* routers exchange neighbour information
* split horizon: avoid anouncing stuff back to the originating link (http://en.wikipedia.org/wiki/Split_horizon [citation needed])
* when routes go down: 2 different ways:
** router senses connection dropped and announces this to his neighbours
** every router will periodically test all known routes
* 2 types ways of keeping & communicating routing data: http://en.wikipedia.org/wiki/Interior_gateway_protocol#Types_of_Interior_gateway_protocols
** link state: has info about all network topology -- so every node in the network knows _the full_ network topology.
:: > Huge amounts of info for large networks. OSPF areas are useful to split this info.
** path vector: contains info ONLY about direct link reachability. (RIP, EIGRP)

BAS: Broad Band Access. Other end of ppoe/a connection used by your DSL line.
IGP: internal gateway protocol: the routing protocol in use on the core network
EGP: external gateway protocol (BGP)

the next hop
fib (ex: MPLS LDP) needs an IGP to determine path cost information.

== What makes the internet tick ==

=== troubleshooting ===

tips'n tricks

* never ever use fw-rules on yr routers

* you can't ping ${some_node}
** lookup yr next hop in yr routing table and try to ping this
** check the return path! (it's always the fucking return path!)
*** check the return path by looking hop-for-hop, to the next hop.
*** routes from and to might be not the same due to bad config

=== BGP ===
ibgp : internal bgp: what we're talking bout here
ebgp : external bgp : the global routing table

all routers connected via bgp sessions, permanently alive (keepconnections to their neighbours open, constant updates)
convergence time: time you need to get an update to _all nodes in yr network (so basically depends on longest path in network) -- should be a couple of seconds max on good network

iBGP allows for filtering:
* able to define which routes get announced and which not - not possible in OSPF
* why should we never filter in OSPF: every node has the topology, when you filter, parts of the topology will be missing -> will create route-loops etc...
** IBGP does not deal with next-hops so route-loops will not be created there

usually you'll run iBGP together with OSPF (OSPF as IGP to resolve next-hop problem)

=== IS-IS ===
http://en.wikipedia.org/wiki/IS-IS

Alternative for OSPF-IGP in this context: IS-IS (more upcoming, better than OSPF). Embarrasingly comming forth out of the OSI 7-layer construct.

ISIS to resolve next hops
IBGP for everything else

=== Testing it all out ===

* There is a possibility to use http://www.gns3.net/ to make virtual router network configurations.
* We are probably going to set up a gettogether to play with GNS3

← Older revision		Revision as of 18:14, 3 October 2010
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	== The 7-layer burrito ==		== The 7-layer burrito ==
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← Older revision		Revision as of 16:22, 3 October 2010
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−	~~= Talk notes =~~
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	== The 7-layer burrito ==		== The 7-layer burrito ==
	layers		layers

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 payload can be ip-packet
 with in there another ip-packet (like a tunnel)
-how to fit that into
+-- how to fit that into:
 === 7 layers of crap ===

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 == The 7-layer burrito ==
-let's say you get ethernet-frame
 in there vlan-tag
 in the payload can be another vlan tag
 payload can be ip-packet
 with in there another ip-packet (like a tunnel)
 === 7 layers of crap ===

@@ Line 171: / Line 171: @@
 === BGP ===
-ibgp : internal bgp: what we're talking bout here
+* ibgp : internal bgp: what we're talking bout here
-ebgp : external bgp : the global routing table
+* ebgp : external bgp : the global routing table
@@ Line 185: / Line 185: @@
 usually you'll run iBGP together with OSPF (OSPF as IGP to resolve next-hop problem)
 === IS-IS ===

Networking talk/Notes - Revision history

2001:6F8:147F:42:88C1:76FF:FE44:6CCE: /* The 7-layer burrito */

2001:6F8:147F:42:88C1:76FF:FE44:6CCE: /* The 7-layer burrito */

2001:6F8:147F:42:88C1:76FF:FE44:6CCE: /* BGP */

Jeroen De Dauw at 18:14, 3 October 2010

Jeroen De Dauw: /* Talk notes */

78.22.102.245: Created page with "= Talk notes = == The 7-layer burrito == layers let's say you get ethernet-frame in there vlan-tag in the payload can be another vlan tag payload can be ip-packet with in there..."