chap 6. ip addressing

6.1 Introduction

	in_ifaddr
		ifaddr generic form
	sockaddr_in 
		sockaddr generic form

network interfaces are assigned IP addresses

5 classes, A, B, C, D, E
D is multicast 224.0.0.1 ...

IP multicast means IP multicast addresses ... not ethernet
	level multicast

	not covering IP multicast routing issues here

Typographical conventions for IP

	Figure 6.1 note ranges

you are either a host or a router (or both)

	host typically has single interface

	router typically has multiple interfaces
		forwards pkts from one if to another over L3

	you can have multiple i/fs and not route
		redundancy consideration
		"virtual web pages"

	bsd ... you are a router if kernel global ipforwarding is set:

	# sysctl -a ... | grep forwarding
		net.inet.ip.forwarding: 0

	# sysctl -w net.inet.ip.forwarding=1

	ipforwarding = 0, means you do NOT route
	ipfowarding = 1, means you do route

/etc/rc.conf
	gateway_enable="YES"  sets the ipforwarding switch as above
	not the default ...

6.2 code intro

	netinet/in.h - Internet address defs
		e.g., def of IP protocol numbers (UDP is 17)
		IPPORT_RESERVED 1024 (< reserved for root services)
		class masks (IN_CLASSD(i))
		socket address, struct sockaddr_in
		setsockopt options
		inet sysctl info
		some kernel function prototypes and macros
	netinet/in_var.h - Internet interface definitions
		in_ifaddr - one allocated per IP on interface
		macros ... for mapping if to IP
		multicast address structure
	netinet/in.c - Internet init and utility functions
		basic ops on IP addresses 
		and internet ioctls
	net/if.c - interface utility functions
	net/if_var.h NOTE: book ignores this
		struct ifaddr exists in here which is GENERIC
		version of "address" structure (points to in_ifaddr)

globals
	in_ifaddr / struct in_ifaddr * /  head of in_ifaddr structure
	in_interfaces - number of ip capable interfaces

Figure 6.5 interface and address data structures

	ifnet -> pts to interfaces
	ifnet_addrs -> pts to global address list

6.4 sockaddr_in structure

	Figure 6.6 sockaddr_in

	Figure 6.7 sockaddr and sockaddr_in line up

6.5 in_ifaddr structure

	one per ip address allocated

6.6 address assignment

	Figure 6.9 ... example network, 

	note: netmask is side of class part of "net", class A/B/C

Figure 6.10 interface ioctl command list

	never mind how you get there! ...  

	end up at in_control for IP ioctl commands

Figure 6.13 in_control function

	if ifp set
		find 1st ip address for that i/f

	do preconditions

	do commands

note:

	note: how command may be passed to interface
		for interface specific functionality (not used
		at this time)

	figure 6.14  
		precondition testing

	if ia is NULL, ... need a new address

	malloc it

	plug ptr into kernel general list

	plug into per if list

	plug ptrs into generic version of structure

Note figure 6.15 ...

siocsifaddr - now actually do it ...

	call in_ifinit to do that work

	ifp ptr, ia ptr, socket ip, scrub

	scrub - delete routes associated with this i/f

	note if ioctl causes it to be passed up to ether_ioctl
		where 
			if_init is called
				device driver HARD reset.  why?
				E.g., you need to turn promiscuous mode off
			arp_ifinit(ifp,ifa) is called
				grat. arp
	
	scrub route bindings ...

#ifconfig wi0
wi0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        inet 10.0.0.1 netmask 0xff000000 broadcast 10.255.255.255
        inet6 fe80::260:1dff:fef0:5203%wi0 prefixlen 64 scopeid 0x8 
        ether 00:60:1d:f0:52:03
        media: IEEE 802.11 Wireless Ethernet autoselect (DS/2Mbps <adhoc>)
        status: associated
        ssid "FreeBSD IBSS" 1:""
        stationname "FreeBSD WaveLAN/IEEE node"
        channel 3 authmode OPEN powersavemode OFF powersavesleep 100
        wepmode OFF weptxkey 1

#netstat -rn ...

"clone route"
ip		   "gateway"
10                 link#8             UC          0        0    wi0

"link-layer route" hanging off of another clone route, note the L
209.180.166.94     00:e0:d0:10:ad:9e  UHLW        3        0    ed0    110

Figure 6-19

	metric (MTU) copied from i/f to address
	if BROADCAST capable i/f
		broadcast is subet | ~subnetmask

	131.252.1.0 | ~255.255.255.0 -> 131.252.1.255

	line 413 ...loopback destination

	Odd ... but likely because BSD algorithm for picking
		ip_src involves looking up likely match for that ip_src
		as ip_dst in the routing table ... thus figure out
		ip_src for IP pkt, and ifp to send it out of.

	install clone route and set flag to indicate that happened

	multicast ...
		put in 224.0.0.1

Figure 6-20
	netmask straight forward

SIOCSIFDSTADDR
		
	dest address assignment for pt. to pt. if, i.e., the other guy

	ME ----------------------- PEER

	241 ... pass it to interface ioctl routine

	if route associated
		delete it
		add it

Retrieving interface info

	Figure 6.22/Figure 6.23

	gets are straight forward

	set is straight forward too ...

Multiple IP addresses per interface

now
	# ifconfig wi0 alias ...  or -alias to remove

	e.g., SIOCGxxx SIOCSxxx operatoe only on 1st interface

	what if you want two addresses per i/f

how can these two boxes talk?
	----------------------------------------------------------
	|					|
	1.1.1.1					2.2.2.2
add     2.2.2.1 ...

	SIOCAIFADDR can do it all 
	SIOCDIFADDR to delete

	Figure 6.24 in_aliasreq structure 
		address/broadcast or dst/netmask

	Figure 6.25 assume ia set to 1st ip address 
	and first 2 memberes of in_aliasreq and ifreq are the same 

	with delete we expect we have something to delete ... 
		if search fails, nothing to do

	code falls thru to 6.14 ... note clever or scary use of structures ...

	after that assume we have a newly malloced in_ifaddr structure or
		an old one

	Figure 6.26

	270 assume hostIsNew is true, and change it if it is not true
		len = 0 or address matches

	if mask len, therefore mask
		toss routes
		set mask
	 	
	if pt to pt
		...

	if host is new or mask it new
		init interface

	if broadcast capable, deal with that 

Deleting IP Addresses SIOCDIFADDR

	ia points to in_ifaddr we want to delete
	Figure 6.27
		scrub routes

	delete from interface address list and from in_ifaddr (internet address list)

	claims that deletion occurs here are interesting.  more precisely
	the 1st chunk of code fixes up lists

	IFAFREE deletes the ifa, if ref. counts allow it.

6.7 Interface ioctl processing

	leioctl, slioctl, loioctl.

	Note: just because IOCTL exists, doesn't mean every i/f does something.

	in_ifinit called by SIOCSIFADDR (set ip )
		
	in_ifinit issues SIOCSIFADDR thru i/f's own if_ioctl function

leioctl, Figure 6.28

	SIOCSIFADDR
		we are UP
		if af_inet
			turn the hw on ... good for arp!
			arpwhohas ... (note: this is done upstairs now)

		default:
			init it anyway

note splx around the whole thing ... 

slioctl, Figure 6.29

		up up up (Sorry, Shania)
		slip is IP only

loioctl
		up 

So what does this do:
	# ifconfig ed0 1.2.3.4

	1. potentially gets the netmask wrong!
	2. grat arp
	3. up as side effect
	4. hw reinit
	5. does something to routing table

	# ifconfig ed0 down
	# ifconfig ed0 up
	what does this do?

6.8 internet utility functions

	in netinet/in.c

	in_netof - return network and part of struct in_addr in, set host bits to 0

	in_canforward - can route it in general (not routing lookup)
		not class D/E, loopback, etc.

	in_localaddr - directly connected address

	in_broadcast - is address broadcast as far as if ifp concerned

6.9 ifnet utility functions

	net/if.c

	ifa_ifwithaddr - search ifnet list for interface with matching
		ipaddr, unicast or broadcast

	ifa_ifwithdstaddr - search for destination address

	ifa_ifwithnet - search ifnet and find address on same network as input

	ifa_ifwithaf - same address family

	ifaof_ifpforaddr - returns ifaddr ptr, if a given ifp matches that address

		note: ifa OF ifp for a given address is idea of function name

	ifa_ifwithroute - if we have dst address (route index) as input,
		find associated ifa

	ifunit(char *name) -> return ifnet ptr for 1st interface by name