Digging into the NetBSD Protocol stack and the ANN kernel Applied Research Laboratory

June 2000 MSR Design 1WashingtonWASHINGTON UNIVERSITY IN ST LOUIS

Digging into the NetBSD Protocol stack and the ANN kernel

Applied Research Laboratory

http://www.arl.wustl.edu/arl/projects/msr/netbsd.pdf


Software Architecture (NetBSD)

KernelPlugins

PluginCtl. Unit

Active Plugin Loader

PluginRequestor

Plugin DBController

PolicyController

SecurityGateway

ANNManager

KeyDB

PluginDB

PolicyRules

CodeServerCode

Server

ActiveCode DB

. . .anetd

JavaVM

ANTS

NOSI

PacketClassificationand Routing

IPv4/6Header

Processing

IP Packets

Dri

ver

Dri

ver

Pac

ket

Sche

dule

r

Dri

ver

Dri

ver

Pac

ket

Sche

dule

r

TCP/UDPPE Kernel Space

RSVP/SSPRouting

PE User Space,Switch Controller,& Remote Servers

SAPF Packet

Selector/Dispatcher . . .

. . .

. . .

ActiveFunction

Dispatcher

. . .

. . .. . .

Resource Controller


Software Architecture (NetBSD)

KernelPlugins

PluginCtl. Unit

PacketClassificationand Routing

IPv4/6Header

Processing

Dri

ver

Dri

ver

Pac

ket

Sche

dule

r

TCP/UDP

SAPF Packets

Selector/Dispatcher . . .

. . .

. . .

ActiveFunction

Dispatcher

. . .

. . .. . .

Resource Controller

IP Packets

• Std. proc. for “plain” IP packets.– classification & routing, header processing, output queueing

• Active packets move through configured kernel plugins.» active function dispatcher passes packets to instances of plugin objects» instantiates objects or triggers download of plugin class, as needed

• streamlined processing of SAPF packets using pre-established state


IP Packets (rfc 791)L

LC

/S

NA

PIP

Hea

der

AA

L5

Tra

iler

IP D

ata

gra

m

Fragment offset

Version H-length TOS Total length

Identification flags

TTL protocol Header checksum

Source Address

Destination Address

Options ??

Type (08.00)OUI (00.00)

OUI (00)LLC (AA.AA.03)

IP data (transport header and transport data)

AAL5 padding (0 - 40 bytes)

CPCS-UU (0) CPCS-UU (0) Length (IP packet + LLC/SNAP)

CRC


IP Header Fields (rfc 791)

• Version - support IPv4 (4)• Header Length - Length in 32 bit words (>= 5)• TOS -• Total Length - Length of datagram in octets• Id - Assists in reassembling fragments• Flags - • Fragment Offset - Where fragment belongs, offset is in octets • TTL - router must decrement, if 0 then discard packet• Protocol - UDP/TCP/ICMP/RSVP to name a few• Header Checksum - 16 bit one’s complement of the one’s

complement sum of all 16 bit words in header• Source Address - Sending hosts IP address• Destination Address - Destination hosts IP address

TOS TOS TOS0 DF

MF

TOS TOSTOSTOSTOSTOS0Precedence D T R 0

TOS Precedense Field:111 - Network Control110 - Internetwork Control101 - Critic/ECP100 - Flash Override011 - Flash010 - Immediate001 - Priority000 - RoutineRemaining TOS Fields:D - 1 = Low delayT - 1 = High ThroughputR - 1 = High ReliabilityDF - 1 = Don’t Fragment,

MF - 1 = More Fragments


Requirements for IPv4 Routers(RFC 1812)

• XX


Active Packet

Type ID=DANVersion (2) F lags

32 b its

AN EP H eader Length (2) AN EP Packet Length

0x8002001

R eserved Length (12)

W aveV ideo TAG

ANEP

DAN

Version (1)

IPv4 header (P ro toco l=A N E P )

N ext H eader=U D P

Source Port D estination Port

U D P checksumU D P lengthUDP

W aveV ideo D ata

0x8002001 (Plugin ID)

Plugin ID in packet ==> NO FILTERS!!


ipintrq:

ipintrip_forward ip_output

ip6_forward ip6_output

atmc_input

apic_isr apic_intr

ip6_input

atmc_output

input packets interrupts output packets

TRANS

tcp/udp_input tcp/udp_output

socket layer

PORT

apic_devoutput

IP Packet Handling in ANN Kernel (APIC)

LINK

DATA

NETWORK

UPPER

LOWER

apic_start

packet_scheduler

PS_Q

sgate

dgate

Fast path



• Device Driver -- Device Dependent – apic_intr ()

• read INTR_ACK: 0 => not for us, return

• apic_isr ()

– apic_isr ()• read NOTIFY_LIST, next rcv channel needing attention

– Process descriptors for RCV channel» swap words in each received mbuf (APIC BUG)

» link mbufs until we find end of frame

» verify CRC (just check flag set by APIC)

» atmc_input(packet)

» repeat

– repeatipintrq:


atmc_input

apic_isr apic_intr

atmc_output

apic_devoutput



• Device Driver - Dev. Independent atmc_input():– LLC/SNAP processing (if needed)

• extract type (IP/RATM/…)

– AAL5 processing• extract length

• strip trailer

– if gateway and !crossbow• ipflow_fastforward()

– aiu_getafix(packet)• aiu_getafix stores a ptr to FTE in packet

– aiu_fastforward(packet)• currently commented out. WHY?

– Enqueue in IP Queue

ipintrq:


atmc_input

apic_isr apic_intr

atmc_output

apic_devoutput


atmc_input()If (interface is not UP), then release mbuf and return

// get packet ethertype

if (LLC/SNAP) then get ethertype from LLC/SNAP header

else use value stored in vc entry (vc->vc_etype)

if (AAL type for this VC (vc->vc_aal) == AAL5) then // strip off trailer

locate last mbuf and get packet length

remove padding and trailer (packet length - mbuf data length)

if (ethertype == IP) try NetBSD/CB fastpath -- not configured in ANN

aiu_getafix() // check flow table for entry (for this packet)

// if one is found then store pointer in mbuf

// else add new entry and cache pointer in mbuf

scheduler software interrupt for IP (ipintr())block interruptsplace packet on IP queueunblock interrupts; return



• IP Input -- ipintr():– Get next packet from IP Queue

– Do some basic checks, header, length, checksum…

– process IP options• Source Route, Record Route, Timestamps

– aiu_dgate(&m,2) Router Plugins Dynamic Gate #2

– if packet is not for us and we can forward it:• forward packet ip_forward() -- upcoming slide...

• return

– aiu_dgate(&m,4) Router Plugins Dynamic Gate #4

– protocol specific input routine e.g. tcp_input()

ipintrq:ipintr ip_forward ip_output

atmc_input

apic_isr apic_intr

atmc_output

apic_devoutput


ipintr() - 1While packets in the IP queue loopblock interruptsget next packet from IP queueunblock interrupts

if (mbuf->len < IP header size) then pullup (mbuf, (IP header size))

if (bad packet IP version), then drop packet and continue

if (receiving interface is NOT configured with an address), then

drop packet and continue

if (ip_hdr->header_length < IP header length) then

drop packet and continue

if (ip_hdr->header_length > mbuf data length) then

pullup(mbuf (ip_hdr->header_length)

if (bad ip_hdr header checksum) then drop packet and continue

if (ip_hdr->total_length < ip_hdr->header_length) then drop and continue

if (mbuf->pkt_length < ip_hdr->total_length) then drop and continue

<continued>


ipintr() - 2if (mbuf->pkt_length > ip_hdr->total_length) then adjust mbuf (trim)

if (IP options are present), then process them

if (ip_hdr->protocol == RSVP) then deliver local

aiu_dgate(2) // Crossbow gate number 2

if (packet destination address matches us -- unicast and broadcast) then

deliver locally

if (multicast destination address) then

if (mbuf uses external buffers) then

mpullup(mbuf, ip_hdr->header_length)

call ip_mforward()

if (ip_hdr->protocol == IGMP) then deliver local

if (local host belongs to mcast group) then deliver local

if (forwarding enabled) then

ip_forward ()

repeat loop



• IP Forwarding -- ip_forward():– decide if we need to send any redirects to sender

– ip_output()

• IP Output -- ip_output()– aiu_dgate(&m,3) Router Plugins Dynamic Gate #3

– get route

– check for special processing• ANEP Options

– anep_output()» if DAN then afd_handle_dan_packet() :ACTIVE PROCESSING

– send on interface

ipintrq:


atmc_input

apic_isr apic_intr

atmc_output

apic_devoutput


ip_forward () - 1

If (broadcast destination address) then drop and return

if (ip_hdr->ttl <= minimum value) then

drop and send ICMP error to source address

decrement ip_hdr->ttl

get cached route // this is a global variable that holds the

// last successful route lookup

if (no cached route || cached route destination != ip_hdr->dest) then

rtalloc(&global_cached_route); // lookup route

if (no route found) then send ICMP error

save copy of packet header // used to create cached flow entries (NetBSD)

// if pkt successfully forwarded. Also used for

// generating ICMP messages if forwarding fails

<continued>


ip_forward ()

if (forwarding to received interface && not source routed &&

source send directly to us && not using default route && route not set by a redirect) then

send ICMP redirect

error = ip_output()

// ip_output (mbuf, 0, &cached_route, IP_FORWARDING, 0);

if (error in ip_output) then

ICMP message Redirect (Host), Unreachable (Host, Needs Fragmentation)

else

if CAN FASTFORWARD then cache flow

return


ip_output () - 1

Process variable length argument list

if (IP options requested) then insert them

if (IP header not filled in) then initialize it

aiu_dgate (mbuf, 3) // Crossbow gate 3

// Verify route is still valid

if NOT (route not null && interface is up&& rotue->dest == ip_hdr->dest) then

lookup route

get interface pointer (ifp) from route entry

If (destination address is multicast) then

process multicast packet // only applicable for packets originating on local host

If (destination is a broadcast address) then

verify interface can handle this (check flags)

<continue>


ip_output () - 2

aiu_findfix() // cache route in flow table

if (ip_hdr->protocol == ANEP) then anep_output(mbuf);

if (ip_hdr->total_length < ifp->mtu) then

ip_hdr->checksum = calculate header checksum

amtc_output (ifp, mbuf, dest, route)

else if (fragmentation allowed) then

fragment packet and link all fragments together (mbuf chains)

block interrupts

if (output interface queue is smaller then number of fragments) then

drop packet and return

unblock interrupts

return

call atmc_output() for each fragment

return



• Device Driver Device Indep.-- atmc_output():– LLC/SNAP processing

– AAL5 processing (if needed)

– if packet_scheduling: enqueue for PS

– if !packet_scheduling: send to devoutput()

• Device Driver Device Dep. -- apic_devoutput()– configure an APIC descriptor for each mbuf in packet

– Resume APIC TX channel

ipintrq:


atmc_input

apic_isr apic_intr

atmc_output

apic_devoutput


amtc_output ()

Verify interface is UP // check flags

if (supplied route is marked as down) then lookup route

extract vpi/vci from route entry

if (simplex interface and broadcast) then use loopback

// gives us a copy

lookup VC specific data struct (atm_vc) using vpi/vci (32 bit int)

hash into array, then linked list

// add LLC/SNAP header

prepend 8 bytes and copy LLC/SNAP field values

// Do ATM AAL5 processing

if (packet is too big (16 bits for size)) then

drop and return

add AAL5 trailer // padding and length

<continue>


amtc_output ()

If (packet scheduling) then

add VPI/VCI to header (prepend 8 bytes to mbuf)

block interrupts

call crossbow PS gate // staticps_enq_gate()

unblock interrupts

else

block interrupts

atm_devoutput()

unblock interrupts

return

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Digging into the NetBSD Protocol stack and the ANN kernel Applied Research Laboratory

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