44100113: COMPUTER NETWORKS FALL 2023 - Project 2: Build Your Own Router
44100113-0: COMPUTER NETWORKS FALL 2023
Build Your Own Router
Assigned: December 6, 2023 Due Date: 23:59, December 27, 2023
1 ASSIGNMENT
You must work on this assignment individually.
This project is designed for you to:
• Learntobuildasimplerouter.
• TobefamiliarwithIPv4,ICMPandARP.
In this project, you will be writing a simple router with a static routing table. Your router will receive raw Ethernet frames and process them just like a real router: forward them to the correct outgoing interface, create new frames, etc. The starter code will provide the framework to receive Ethernet frames; your job is to create the forwarding logic.
You are allowed to use some high-level abstractions, including C++11 extensions, for parts that are not directly related to networking, such as string parsing, multi-threading, etc.
In the following contents, you will see
• DetaileddescriptionofthisporjectinSection2
• GuidelinestosetuptheenvironmentinSection3
• OverviewofthestartercodeinSection4
• SomehelpfulhintsinSections5
• HowtosubmityourcodeinSection6
• GradingcriteriainSection7
This assignment is considerably hard, so get started early, not as some of you did for FTP Project, to avoid missing the deadline.
1
2 PROJECT DESCRIPTION
There are four main parts in this assignment:
• HandleEthernetframes
• HandleARPpackets
• HandleIPv4packets
• HandleICMPpackets
This assignment runs on top of Mininet which was built at Stanford. Mininet allows you to emulate a network topology on a single machine. It provides the needed isolation between the emulated nodes so that your router node can process and forward real Ethernet frames between the hosts like a real router. You don’t have to know how Mininet works to complete this assignment, but if you’re curious, you can learn more information about Mininet on its official website (http://mininet.org/).
Your router will route real packets between emulated hosts in a single-router topology. The project envi- ronment and the starter code has the following default topology:
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+−−−−−−−−−−−−−−−−+ server1−eth0 |
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192.168.2.1/24 | sw0−eth1 | +−−−−−−−−−−+ +−−−−−−−−−−−−−−−−−−+ | | server1 | | | | | | +−−−−−−−−−−−+ | SimpleRouter | |
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+−−−−−−−−−−+ client −eth0 | | 10.0.1.100/8 + sw0−eth3 sw0−eth2 10.0.1.1/8 172.64.3.1/16 | | | server2 | |++|| |
|
| | | +−−−−−−−−−−−+ | | | server2−eth0 +−−−−−−−−−−−−−−−−−−−−−−+ +−−−−−−−−−−−−−−−−+ 172.64.3.10/16 |
The corresponding routing table for the SimpleRouter sw0 in this default topology:
NOTE: DonothardcodeanyIPaddresses,network,orinterfaceinformation.Wewillbetestingyour code on other single-router topologies with different number of servers and clients, and different IP and network addresses. So it is STRONGLY RECOMMENDED that you test your implementations under dif- ferentIPaddressesandroutingtables(bymodifyingthe IP_CONFIG and RTABLE filerespectively).
If your router is functioning correctly, all of the following operations should work:
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Destination Gateway Mask Iface −−−−−−−−−−−− −−−−−−−−−−−− −−−−−−−−−−−−−−−− −−−−−−−− |
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0.0.0.0 192.168.2.2 172.64.3.10 10.0.1.100 0.0.0.0 0.0.0.0 255.255.255.0 0.0.0.0 255.255.0.0 sw0−eth3 sw0−eth1 sw0−eth2 |
2
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ping fromtheclienttoanyoftherouter’sinterfaces:
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mininet> client ping 192.168.2.1 |
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... ... ... |
•
•
•
•
ping fromtheclienttoanyoftheappservers:
from the client to any of the router’s interfaces:
from the client to any of the app servers:
Downloadingfilesfromhttp-serverby wget command
2.1 ETHERNET FRAMES
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mininet> client ping server1 # or client ping 192.168.2.2 ... mininet> client ping server2 # or client ping 172.64.3.10 |
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... |
traceroute
mininet> client traceroute 192.168.2.1 ...
mininet> client traceroute 172.64.3.1
...
mininet> client traceroute 10.0.1.1
...
traceroute
mininet> client traceroute server1
...
mininet> client traceroute server2
...
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mininet> client wget http://192.168.2.2/<filename> |
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... ... |
A data packet on a physical Ethernet link is called an Ethernet packet, which transports an Ethernet frame as its payload.
The starter code will provide you with a raw Ethernet frame. Your implementation should understand source and destination MAC addresses and properly dispatch the frame based on the protocol.
0123 01234567890123456789012345678901 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+
| Destination Address | + (48 bits ) +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+
3
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| | Source Address | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ (48 bits ) + || +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Type (16 bits) | | |
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+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ + || || ~ Payload ~ || || |
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+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ |
Note that actual Ethernet frame also includes a 32-bit Cyclical Redundancy Check (CRC). In this project, you will not need it, as it will be added automatically.
• Type : Payload types – 0x0806 (ARP)
– 0x0800 (IPv4)
For your convenience, the starter code defines Ethernet header as an structure in :
Requirements
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YourroutershouldignoreEthernetframesotherthanARPandIPv4.
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Your router must ignore Ethernet frames not destined to the router, i.e., when destination hard- ware address is neither the corresponding MAC address of the interface nor a broadcast address ( FF:FF:FF:FF:FF:FF ).
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Your router must appropriately dispatch Ethernet frames (their payload) carrying ARP and IPv4 packets.
2.2 ARP PACKETS
The Address Resolution Protocol (ARP) (RFC 826) is a telecommunication protocol used for resolution of Internet layer addresses (e.g., IPv4) into link layer addresses (e.g., Ethernet). In particular, before your router can forward an IP packet to the next-hop specified in the routing table, it needs to use ARP re- quest/reply to discover a MAC address of the next-hop. Similarly, other hosts in the network need to use ARP request/replies in order to send IP packets to your router.
Note that ARP requests are sent to the broadcast MAC address ( FF:FF:FF:FF:FF:FF ). ARP replies are sent directly to the requester’s MAC address.
ethernet_hdr
core/protocol.hpp
struct ethernet_hdr {
uint8_t ether_dhost[ETHER_ADDR_LEN]; /* destination ethernet address */
uint8_t ether_shost[ETHER_ADDR_LEN]; /* source ethernet address */
uint16_t ether_type ; /* packet type ID */ } __attribute__ ((packed)) ;
4
|
0123 01234567890123456789012345678901 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Hardware Type | Protocol Type | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ |
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| HW addr len | Prot addr len | Opcode | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ || ~ Source hardware address ~ || +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ |
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|| ~ Source protocol address ~ || +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ || |
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~ Destination hardware address ~ || +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ || ~ Destination protocol address ~ || |
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+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ |
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Hardware Type : 0x0001 (Ethernet)
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Protocol Type : 0x0800 (IPv4)
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Opcode :
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– 1 (ARP request)
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– 2 (ARP reply)
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HW addr len : number of octets in the specified hardware address. Ethernet has 6-octet addresses,
so 0x06.
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Prot addr len : number of octets in the requested network address. IPv4 has 4-octet addresses, so 0x04.
For your convenience, the starter code defines the ARP header as an structure in :
struct arp_hdr
arp_hdr
core/protocol.hpp
{
unsigned unsigned unsigned unsigned unsigned
short short char char short
arp_hrd ; arp_pro ; arp_hln ; arp_pln ; arp_op ;
/* format of hardware address */ /* format of protocol address */ /* length of hardware address */ /* length of protocol address */ /* ARP opcode (command) */
unsigned char
uint32_t
unsigned char
arp_sha[ETHER_ADDR_LEN]; /* sender hardware address arp_sip ; / * sender IP address arp_tha[ETHER_ADDR_LEN]; /* target hardware address arp_tip ; /* target IP address
*/ * / */ */
uint32_t
} __attribute__ ((packed)) ;
5
Requirements
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YourroutermustproperlyprocessincomingARPrequestsandreplies:
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– MustproperlyrespondtoARPrequestsforMACaddressfortheIPaddressofthecorrespond- ing network interface
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– MustignoreotherARPrequests
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When your router receives an IP packet to be forwarded to a next-hop IP address, it should check
ARP cache if it contains the corresponding MAC address:
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– Ifavalidentryfound,theroutershouldproceedwithhandlingtheIPpacket
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– Otherwise,theroutershouldqueuethereceivedpacketandstartsendingARPrequesttodis- cover the IP-MAC mapping.
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When router receives an ARP reply, it should record IP-MAC mapping information in ARP cache (Source IP/Source hardware address in the ARP reply). Afterwards, the router should send out all corresponding enqueued packets.
NOTE: Your implementation should not save IP-MAC mapping based on any other messages, only from ARP replies!
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ToreducestalenessoftheARPinformation,entriesinARPcacheshouldtimeoutafter 30seconds. Thestartercode(ArpCache class)alreadyincludesthefacilitytomarkARPentries“invalid”.Your task is to remove such entries. If there is an ongoing traffic (e.g., client still pinging the server), then the router should go through the standard mechanism to send ARP request and then cache the response. If there is no ongoing traffic, then ARP cache should eventually become empty.
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TheroutershouldsendanARPrequestaboutonceaseconduntilanARPreplycomesbackorthe requesthasbeensentoutatleast 5times.
If your router didn’t receive ARP reply after re-transmitting an ARP request 5 times, it should stop re-transmitting, remove the pending request, and any packets that are queued for the transmission that are associated with the request.
YourroutershouldalsosendanICMPDestination HostUnreachable messagetothesourceIP.
2.3 IPV4 PACKETS
Internet Protocol version 4 (IPv4) (RFC 791) is the dominant communication protocol for relaying data- grams across network boundaries. Its routing function enables internetworking, and essentially estab- lishes the Internet. IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram with source and destination information.
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0123 01234567890123456789012345678901 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ |
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| Version | IHL | Type of Service | Total Length | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ |
6
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| Identification | Flags | Fragment Offset | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Time to Live | Protocol | Header Checksum | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Source Address | |
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+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Destination Address | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Options | Padding | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ || |
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|| ~ Payload ~ || || +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ |
For your convenience, the starter code defines the IPv4 header as an structure in :
uint8_t uint16_t
ip_tos ; ip_len ;
*/
service */
ip_hdr
core/protocol.hpp
struct ip_hdr {
unsigned int ip_hl :4; unsigned int ip_v :4;
/* header
/* version
/* type of
/* total length */
length */
uint16_t
uint16_t
uint8_t
uint8_t
uint16_t ip_sum;
/* identification */
/* fragment offset field */
/* time to live */
/* protocol */
/* checksum * /
ip_id ;
ip_off ; ip_ttl ; ip_p ;
uint32_t ip_src , ip_dst ; /* source and dest address */ } __attribute__ ((packed));
Requirements
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ForeachincomingIPv4packet,yourroutershouldverifyitschecksumandtheminimumlengthof an IP packet
– Invalidpacketsmustbediscarded.
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Your router should classify datagrams into (1) destined to the router (to one of the IP addresses of
the router), and (2) datagrams to be forwarded:
– For(1),ifpacketcarriesICMPpayload,itshouldbeproperlydispatched.Otherwise,discarded (a proper ICMP error response is NOT required for this project).
– For (2), your router should use the longest prefix match algorithm to find a next-hop IP ad- dress in the routing table and attempt to forward it there
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For each forwarded IPv4 packet, your router should correctly decrement TTL and recompute the checksum.
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2.4 ICMP PACKETS
Internet Control Message Protocol (ICMP) (RFC 792) is a simple protocol that can send control informa- tion to a host.
In this assignment, your router will use ICMP to send messages back to a sending host. • Echo or message
Echo Reply
0123
01234567890123456789012345678901 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Type | Code = 0 | Checksum | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+
| Identifier | Sequence Number |
+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Data ...
+−+−+−+−+−
– Type
* *
8 : echo message
0 : echo reply message
message
Time Exceeded
0123
01234567890123456789012345678901 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Type=11 | Code | Checksum | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+
| unused | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Internet Header + 64 bits of Original Data Datagram | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+
•
– Code
* *
0 : time to live exceeded in transit
1 : fragment reassembly time exceeded (NOT required to implement)
message
Destination Unreachable
0123
01234567890123456789012345678901 +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+
| Type=3 | Code | Checksum | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | unused | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+ | Internet Header + 64 bits of Original Data Datagram | +−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+−+
•
8
– Code
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* 1 : Destination host unreachable
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* 3 : Destination port unreachable
When an ICMP message is composed by a router, the source address field of the internet header can be the IP address of any of the router’s interfaces, as specified in RFC 792.
Notethat TimeExceeded messageisneededfor traceroute toworkproperly.
For your convenience, the starter code defines the ICMP header as an structure in :You may want to create additional structs for ICMP messages, but make sure to use the packed attribute so that the compiler doesn’t try to align the fields in the struct to word boundaries (i.e., must use
__attribute__((packed)) annotation).
Requirements
Your router should properly generate the following ICMP messages, including proper ICMP header check- sums:
icmp_hdr
core/protocol.hpp
struct icmp_hdr { uint8_t icmp_type ; uint8_t icmp_code;
uint16_t icmp_sum;
} __attribute__ ((packed));
•
•
•
Echo Reply message ( type 0 ):
Sent in response to an incoming Echo Request message (ping) to one of the router’s interfaces.
Echo requests sent to other IP addresses should be forwarded to the next hop address as usual. Inthisproject, EchoReply message’sinitialTTLfieldinitsIPv4headershouldbe 64.
Time Exceeded message ( type 11 , code 0 ):
Sent if an IP packet is discarded during processing because the TTL field is 0. This is needed for
traceroute to work.
Port Unreachable message ( type 3 , code 3 ):
Sent if an IP packet containing a UDP or TCP payload is sent to one of the router’s interfaces. This is needed for traceroute to work.
3 ENVIRONMENT SETUP
You are suggested to finish this project on Ubuntu 16.04.7. If your system is Windows or Mac OS, you can install Ubuntu 16.04.7 Virtual Machine in VMware. (Do not use Windows Subsystem for Linux (WSL), as Mininet is currently not supported by WSL.)
We provide to setup the environment. Please run it in superuser mode:
setup.sh
sudo bash setup.sh
9
To run or test your code, please change work path to the project directory and open three terminals here, then
-
inthefirstterminal,startpox
/opt/pox/pox . py −−verbose ucla_cs118
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inthesecondterminal,startMininet chmod +x run.py
sudo ./run.py
To exit Mininet, type exit command in this terminal.
3. inthethirdterminal,startyourrouter
Besides,youcanusethe show-arp.py scripttoprintoutyourrouter’scurrentarpcacheorroutingtable in another terminal.
• Toshowarpcahce,run:
./show−arp.py arp
• Toshowroutingtable,run:
./show−arp.py routing
Here are some tips:
-
DONOTCOPYdirectlyfromtheprojectspec,asthepdfformattingmaybeproblematic.
-
Ifyougetthefollowingoutputsafterrunningrouter
or
Please restart Mininet.
-
Ifyougetthefollowingoutputsafterrunning
Maybe converting the format of is helpful
make
./ router
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Got packet of size 42 on interface sw0−eth1 |
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Received packet, but interface is unknown, ignoring |
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Resetting SimpleRouter with 0 ports |
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Interface l i s t empty |
run.py
/usr/bin/env: ’python\r ’ : No such file or directory
run.py
sudo apt−get install dos2unix dos2unix run.py
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• •
When POX controller is restrated, the simpler router needs to be manually stopped and started again.
Ifyougetthefollowingoutputsafterrunning or
Try cleaning up mininet related environments by
sudo mn −c
4 STARTER CODE OVERVIEW is the overal structure of the starter code:
Here
|
simple−router .hpp || |
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|| +−−−+−−−−−+−−−−+ m_arp 1 | 1| | 1 m_ifaces +−−−−−−−−−−−−−−−−+ | +−−−−−−−−−−−−−−−−−−+ ||| |
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| | m_routingTable |
||| vvv +−−−−−−+−−−−−+ +−−−−−−+−−−−−−−+ +−−−−−+−−−−−+ |||||| |
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| ArpCache | | RoutingTable | | Interface | |||||| +−−−−−−−−−−−−+ +−−−−−−−−−−−−−−+ +−−−−−−−−−−−+ arp−cache.hpp routing−table .hpp core/interface .hpp |
•
•
•
SimpleRouter
Mainclassforyoursimplerouter,encapsulating ArpCache, RoutingTable,andassetof Interface
objects.
Interface
Class containing information about router’s interface, including router interface name ( name ),
hardware address ( addr ), and IPv4 address ( ip ).
RoutingTable ( routing-table.hpp|cpp )
Class implementing a simple routing table for your router. The content is automatically loaded
fromatextfilewithdefaultfilenameis RTABLE (namecanbechangedusing RoutingTable option in router.config configfile)
•
ArpCache ( arp-cache.hpp|cpp )
Exception : Error creating interface . . . RTNETLINK answers : File exists
run.py
autograde.py
11
•
•
•
Method to send raw Ethernet frames (
Method to handle ARP cache events (
Method to lookup entry in the routing table (
):
Class for handling ARP entries and pending ARP requests.
4.1 KEY METHODS
Your router receives a raw Ethernet frame and sends raw Ethernet frames when sending a reply to the sending host or forwarding the frame to the next hop. The basic functions to handle these functions are:
•
Method that receives a raw Ethernet frame (
):
Need to implement
Implemented
simple-router.hpp|cpp
/**
* This method is called each time the router receives a packet on
* the interface. The packet buffer \p packet and the receiving
* interface \p inIface are passed in as parameters.
*/
void
SimpleRouter::handlePacket(const Buffer& packet, const std::string& inIface);
simple-router.hpp|cpp
/**
* Call this method to send packet \p packt from the router on
* interface \p outIface
*/
void
SimpleRouter::sendPacket(const Buffer& packet, const std::string& outIface);
Need to implement
arp-cache.hpp|cpp
):
/**
* This method gets called every second. For each request sent out,
* you should keep checking whether to resend a request or remove it.
*/
void
ArpCache : : periodicCheckArpRequestsAndCacheEntries ( ) ;
Need to implement
routing-table.hpp|cpp
):
/**
* This method should lookup a proper entry in the routing table
* using " longest −prefix match" algorithm
*/
RoutingTableEntry
RoutingTable : : lookup ( uint32_t ip ) const ;
4.2 DEBUGGING FUNCTIONS
We have provided you with some basic debugging functions in core/utils.hpp ( core/utils.cpp ). Feel free to use them to print out network header information from your packets. Below are some functions you may find useful:
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•
•
•
print_hdrs(const uint8_t *buf, uint32_t length) , print_hdrs(const Buffer& packet) Print out all possible headers starting from the Ethernet header in the packet
ipToString(uint32_t ip) , ipToString(const in_addr& address)
Print out a formatted IP address from a uint32_t or in_addr . Make sure you are passing the IP
address in the correct byte ordering
macToString(const Buffer& macAddr) PrintoutaformattedMACaddressfroma Buffer ofMACaddress
4.3 LOGGING PACKETS
You can use Mininet to monitor traffic that goes in and out of the emulated nodes, i.e., router, server1 and server2. For example, to see the packets in and out of server1 node, use the following command in Mininet command-line interface (CLI):
mininet> server1 sudo tcpdump −n −i server1−eth0
Alternatively, you can bring up a terminal inside server1 using the following command
mininet> xterm server1
then inside the newly opened :
$ sudo tcpdump −n −i server1−eth0
xterm
4.4 GRADING SCRIPT
Toeasedebugging,wemakeasimplifiedversionofgradingscriptpublicwith autograde.py.Itcontains all the public test cases (details in Section 7), which make up 45/85 of the total test score. To run the script, first start pox and your router, then use the following command:
chmod +x autograde.py sudo . / autograde . py
The grading result and related information will be shown in standard output as well as the details.log file. You can also change the logging level to see more detailed information:
log . setLevel ( logging .DEBUG)
If you get the following outputs from router:
Just turn off your router, grading script, and then start and exit Mininet with run.py . Afterwards, the grading script may work as expected.
Got packet of size 42 on interface sw0−eth1 Received packet, but interface is unknown, ignoring
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Notice that the private, comprehensive grading script will be run on other single-router topology with different interfaces, IP/MAC addresses. Thus, the output of provided script may be different from your final score, even on public test cases.
5 HELPFUL HINTS
Given a raw Ethernet frame, if the frame contains an IP packet that is not destined towards one of our interfaces:
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Sanity-checkthepacket(meetsminimumlengthandhascorrectchecksum).
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DecrementtheTTLby1,andrecomputethepacketchecksumoverthemodifiedheader.
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Find out which entry in the routing table has the longest prefix match with the destination IP ad- dress.
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Check the ARP cache for the next-hop MAC address corresponding to the next-hop IP. If it’s there, send it. Otherwise, send an ARP request for the next-hop IP (if one hasn’t been sent within the last second), and add the packet to the queue of packets waiting on this ARP request.
If an incoming IP packet is destined towards one of your router’s IP addresses, you should take the fol- lowing actions, consistent with the section on protocols above:
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If the packet is an ICMP echo request and its checksum is valid, send an ICMP echo reply to the sending host.
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IfthepacketcontainsaTCPorUDPpayload,sendanICMPportunreachabletothesendinghost. Otherwise, ignore the packet. Packets destined elsewhere should be forwarded using your normal forwarding logic.
Obviously, this is a very simplified version of the forwarding process, and the low-level details follow. For example, if an error occurs in any of the above steps, you will have to send an ICMP message back to the sender notifying them of an error. You may also get an ARP request or reply, which has to interact with the ARP cache correctly.
In case you have difficulties, you can contact the TAs by email: zgxw18@gmail.com,ycdfwzy@outlook.com or visit the TAs at 11-211, East Main Building.
6 SUBMISSION REQUIREMENTS
To submit your project, you need to prepare:
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A report.pdf filenomorethanTHREEpages.(Seedetailsinsection7)
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Allyoursourcecode, Makefile and report.pdf asa .tar.gz archive(andanyfilesfromextracredit part).
To create the submission, use the provided Makefile in the starter code. Just update Makefile to include your student ID and then just type
make tarball
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Then submit the resulting archive to WEB LEARNING. Before submission, please make sure:
• • •
Yourcodecompiles Yourimplementationconformstothespecification
.tar.gz archivedoesnotcontaintemporaryorotherunnecessaryfiles.Wewillautomaticallydeduct points otherwise.
7 GRADING GUIDELINES
Yourprojectwillbegradedbasedonthefollowingparts(privatetestsarenotprovidedin autograde.py): 1. Pingtests
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a) (5 pts, public) Pings from client to all other hosts (all pings expected to succeed), including non-existing host (error expected)
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b) (5 pts, public) Pings from server1 to all other hosts (all pings expected to succeed), including non-existing host (error expected)
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c) (5 pts, public) Pings from server2 to all other hosts (all pings expected to succeed), including non-existing host (error expected)
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d) (10pts,private)Pingresponses(fromclient)haveproperTTLs
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e) (5pts,public)Pingbetweenselectedhosts,checkARPcache,thereshouldbeapropernum- ber of entries
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f) (5pts,public)Pingfromclienttoserver1,after40seconds,theARPcacheshouldbeempty(+ no segfaults)
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g) (5 pts, private) Ping from client a non-existing IP, router sends proper ARP requests (+ no segfaults)
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h) (5pts,private)Pingfromclient,receivehostunreachablemessage
2. Traceroutetests
a) (5pts,public)Traceroutefromclienttoallotherhosts,includinganon-existinghost b) (5pts,public)Traceroutefromserver1toallotherhosts,includinganon-existinghost c) (5pts,public)Traceroutefromserver2toallotherhosts,includinganon-existinghost
d) (10pts,private)Traceroutefromclienttorouter’sinterfaces(get1line) 3. Filedownloadingtests
a) (5pts,public)Downloadasmallfile(≈1KB)fromanyserverthroughhttp
b) (10pts,private)Downloadalargefile(≈10MB)fromanyserverthroughhttp 4. (20pts)CodequalityandProjectReport(report.pdf)
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The project report could include:
a) YournameandstudentID
b) Theproblemsyouhavemetinthisprojectandhowyousolvedthem.
c) Listofanyadditionallibrariesused. d) Anyadviceonthisproject.
Note that poor design, code structure, or report will probably reduce the credits you gained in this part.
Suppose you get A credits according to the above criteria, your final grade should be
8 ACKNOWLEDGEMENT
This project is based on the CS118 class project by Alexander Afanasyev, UCLA.
