aml.ca ciprofloxacn and beer chen-liu.com can i take lexapro while weaning of pristiq linezolid price colombia vitimines to increase thyroxine levels occasional use of advil with celebrex menstrual cycle lasix lisinopril without water pill ketoconazole long term use viagra vgr 100 street value cymbalta going from 30am 30pm to 30am to 60 pm alguien ke venda misoprostol en aguascalientes cherries and erectile dysfunction how many milligrams can u go on clonidine africanamericanimages.us cytotec santa marta what is a natural alternative to bactrim fluconazole kegunaan mirtazapine actavis wiki MASTERRAFTING.COM buy zofran odt online springracinginsights.com disabledinafghanistan.com augmentin 625 mg price india for 6 tablets eloco.pl hanhvyshop.vn atarax et migraine is it ok to take 0.4 mg flomax twicw a day where can i find cytotec in zimbabwe does cipro tab cause brown stains after ovulation bactrim 160 mg what to use instead of prednisone for dogs buy valacyclovir hcl online cheap bmmpm.com iud insertion with misoprostol nz linezolid in egypt para que sirve el danazol 100 mg costa allegra cabins mayo clinic lipitor side effects glucophage 500 xr side effects NEOHAIRINDO.COM cialis order in canada buy montelukast uk fehmierduran.com metoprolol mg 25 tamoxifeno oil hair order celexa epc-geophysics.com gabapentin gel dose lisinopril law suit propranolol mg stage fright can levaquin be taken with tamiflu do we give digoxin in cpr order bactrim cream online sinequan 150 mg anybody take 500mg of sertraline a day arman-crusher.com atorvastatin 20 tabletspcshelf life telmisartan substitute sertraline withdrawals zofran for cats tetracycline ointment in india atarax 1g sildenafil citrate 50 mg dosage egyptgolftours.com cowinbuy.com will metronidazole affect my marijuana drug test how often do i use flagyl 500 mg to treat ringworms ncsdsample2.docbro.com covenantofpoppies.com ketoconazole shampoo available in philippines NEOHAIRINDO.COM adalat low price online buy taking escitalopram 20 mg and ritalin stlsoccer.net antibiotic to cover strep and uti metformin online canada viagra pills for women pharmacy in kenya 2exhibitions.com name fur tablet zum depresi zyprexa 20 what is buspirone used for is levaquin removed with hemodialysis escitalopram stopping anxiety and heart palpitations can amoxicillin capsules and piritin tap cure infection hyzaar price comparison foodloversheaven.com sertraline hcl 100 mg cost 90 metoprolol succ fluconazole shelf life lasix diuretic for sale puedo tomar cytotec con 25 semana does valtrex work on cold sores sintomas al tomar cytotec para abortar famciclovir ecuador is red yeast rice safe to take with plavix celexa and neurontin side effects of phenergan on cats q2melbourne.com cyproheptadine hydrochloride for kids in uk pastilla xenical tamsulosin keinen samenerguss zocor with lamisil revista 400 can hydrochlorothiazide cause bradycardia what is the difference between cialis 5mg 10 20 an40 does dischem sell xenical pills duloxetine hcl dr 60 mg cap amoxicillin and plasma donation nizoral anti dandruff lotion flipkart diovan 325 mg cymbalta 15mg avastan.pl verapamil 180 mg sa can i take diazepam and phenergan on the same day azithromycin 500mg dosage lamisil lotrimin at naftin and lotrimin ultra in india clomid timeline with doctor appointments is there back conversion for ciprofloxacin thuoc celecoxib capsules 200mg springracinginsights.com terbinafine salep buat inu menyusui mutien.be levaquin 500 mg dosage sinus infection prozac fda approval 1987 seroquel ir and adderall xr valerian.root capsules interaction with lisinopril dataminingweb.com baclofen nursing interventions order albuterol sulfate bactrim es efectivo doxycycline 300g upperbe.it amoxicillin capsules 0.25g prekpektus orlistat n underactive thyroid provera and yellow stool apartamenty-kasztelanskie.pl zovirax crema aciclovir 2g precio pildoras 8163 seroquel cheap propecia online uk sertraline pret hydroxyzine 25 mg high yahoo answers 4kom.it alendronate sodium tablets 70 mg side effects vulvadynia singulair ansbach-direkt.de flagyl cost in india csipropertyservices.com norvasc and snake venom vitaroom.net 555fs.com why does celexa take so long to work prednisone affects l5 s1 que consecuencias causa el cytotec de 200 mcg provera and yellow stool how soon can i take the economy diflucan one dodoku.com coumadin price levitra 10mg price how long does buspar work till next dose amoxicillin tablet can get good sperm amlodipine besylate 5mg buy online generic lipitor problems desogen initial breakout bukitpinus.com metronidazole dose for poultry prednisone dosage for sinus how long after being on azithromycin not contagious sildenafil 100mg uses trying pregnant prescribed apo metformin order flagyl online how long can you keep azithromycin dces.net.pl does thyroxine tablets cause breast cancer michelamarchiotto.com overdose with hydrocodone with augmentin voltaren 1 gel dosage sintomas de la cytotec egyptgolftours.com hanhvyshop.vn directmobility.co.uk can metformin cause constipation during ivf pregnancy how much amoxicillin should i give a 3 year old can misoprostol terminate pregnancy azithromycin 500 dzialanie is levofloxacin 500mg can cure gonorrhea bactrim oral solution dosage how long after flagyl can i breastfeed azithromycin 500mg for treating chlamydia bcbs cialis for bph atenolol and metformin interactions dose of amoxil 875 mg for uti disabledinafghanistan.com ziyinzhuangyang viagra 3000mg porque se usa bactrim forte en purpura balitoursclub.com voltaren 10 provera 20 mg three times daily does prescription amoxicillin 825mg have acetomephene generic atenolol azithromycin kills sperm how to use kamagra prometrium 200 mg to induce period generic viagra prices iranstrick-tiregroup.com fexofenadine 200mg piroxicam y hemorroides n shock herbal viagra reviews can i have a cardiac arrest from zoloft levofloxacin 500ml delite.cn lamisil cream pregnancy sfe levitra 10 mg 4 film tablet can you take benadryl if you take norvasc dosage per kg of phenergan injection 500mg azithromycin vs 1000 mg kamagra oral jelly brisbane how much does zyvox cost prozac 2 weeks alternative of linezolid africanamericanimages.us albuterol 180 mcg em2nt.net cordarone 100 mg using lexapro wellbutrin together azithromycin 1gm packets without perscription bactrim ds 960mg como tomar xenical nitroglycerin kao lek lamisil cream price atomoxetine 100 mg over the counter amlodipine philippines bmmpm.com zyprexa generic manufacturer has anyone taken viagra after stents 4kom.it impact of too much metformin what medicine ciprofloxacin stands for cerisdieventi.com componente de la pastilla piroxicam amoxicillin 500mg trexil for cough 2exhibitions.com can you buy augmentin over the counter in prague minimu safe time beween cialis and alcohol cytotec misoprostol kuala lumpur costco brookfield ct price on bupropion classification for naprosyn 500mg diltiazem ointment in india price cara kerja obat doxycycline can you use doxycycline for infection in canine .. akademia-active.pl cardura 4 mg use sekerpinarosgb.com csipropertyservices.com aasoc.pl hair loss forum finasteride no prescription metronidazole 62.5 mg tablets acyclovir 400 stada metronidazole ip prednisone 40 mg daily 7 day taper dosing schedule california-employment-lawyers.com afdoor.com diflucan 500 not working yeast infection cymbalta cost australia ketoconazole generic philippines viagra price boots can claritin be taken with singulair levitra 5mg enough buy nolvadex tamoxifen indiac shelf life fluconazole is cialis from india real i lost weight with metformin can my 12 year old use ciprofloxacin 500 mg tab north akademia-active.pl smoking weed and taking cialis metronidazole for dogs dosage for diarrhea dexamethasone and bactrim for sinusitis NEOHAIRINDO.COM dopasujbuty.pl flagyl antibiotic how long stay in your system is bloating a side effects of ciprofloxacin 500 mg is augmentin 1000 duo dangerous for ckd patient sertraline and syndol fluconazole and marijuana nizoral 200mg uses celexa farts lamisil and male yeast infection buy wellbutrin xl online from canada cheap xenical pills celebrex 400 mg bid zyvox price malaysia bupropion australia antidepressant can you take ondansetron with excedrin 60mg of accutane uk how much flouride in 40mg of citalopram can you get high off zyprexa montelukast with levocetirizine drug contraindications avastan.pl taking tetracycline for abortion lexapro first days batterymedix.com is amitriptyline hcl 50 mg tab a narcotic want to buy amoxicillin 500mg in uk can i take omeprazole with thyroxine chatcopii.com where to buy ivermectin for chickens butik allegra u beogradu heart palpitations while taking prometrium disabledinafghanistan.com piroxicam b cyclodextrin prices in pakistan cialis daily and adderall propranolol hydrochloride 80 mg for anxiety iranstrick-tiregroup.com montelukast actavis bijwerkingen atenolol 12.5 mg daily bemylight.org dodoku.com sildenafil cost per pill can you take nexium without food lasix 160 mg amlodipine clopidogrel and alcohol diflucan liver toxicity drugprevent.org.uk viagra yellow pills buy viagra tablets apotik yang menjual metronidazole cream metoprololer 100 mg para que sirven carvedilol 6 mg taking motrin cipro and vicodin together is fluconazole safe for 6 months pregnant isotretinoin 20 mg will amoxillin help remove depot shots out of the body buy indomethacin gel telmisartan 50 mg can one eat watermelon while using warfarin can you take diflucan and antibiotics at same time azithromycin capsules treatment for gonorrhea secretlives.me can you overdose on 300mg of trazodone bactrim 200 mg para que sirve delite.cn yalovadaarsa.com puedo comer despues de haber diluido el misoprostol synthroid pills for sale price of plavix 75 mg is four 5mg cialis equal to a reg 20mg cialis linezolid form 1 does taking diazepam interfere with arimidex benefits sampiyonhaliyikama.com peyronies and low dose cialis bmmpm.com viagra abu dhabi amitriptyline prise de poids citalopram hydrobromide 40mg ketoconazole no prescription ok to eat bananas takeing lisinopril what is biotech ciprofloxacin ease for lawonline.co.il will bactrim clear up bv or yeast where to buy over the counter cytotec in cebu city ivermectin lotion price terbinafine dusting powder to face wound efpa-polska.pl comprar tofranil 50 mg aasoc.pl africanamericanimages.us can you drink non alcoholic beer while taking flagyl drconev.pl rapaflow vs flomax yalovadaarsa.com meloxicam for cats uk buy clozapine canada panoramainternetu.pl eczema and prednisone dosage does cyproheptadine slow down metabolism buy maxalt no prescription can toilet infection be treated with amoxil do i take the 400mg flagyl all at once erythromycin stearate bromhexine hcl montelukast 4 mg tablets kastairez bezpieczne-nawierzchnie.pl compare ipratropium and albuterol mayo webmd gelernt.net drconev.pl proscar no prescription bukitpinus.com amlodipine 100mg muallimkoyosgb.com tab augmentin 625 dosage india how often is bupropion hci fail urin test eude.es DORREAJATETXEA.COM terbinafine tablets and microgynon 30 40mg of prednisone for 9 year old buy lisinopril hctz 20 12.5 mg without prescription can i high off of paroxetine net doctor group viagra what does liquid tamoxifen citrate look like audiomaximus.com cialis dosis can clomid drug stop period audiomaximus.com sekerpinarosgb.com price levitra vardenafil zithromax 500mg obat apa escitalopram erowid gabapentin 800 mg tab can i tske tylenol with antibiotics and buscopan can i give my dog metronidazole and what dose prezzo cabergoline misoprostol seaple 1862 venezuela from generic india viagra cena plavix 75 mg strattera albuterol inhaler interaction imipramine cost what is difference between revatio and viagra cytotec aborto 3 meses clopidogrel 600 mg stat cialis paypal celecoxibe nmr allcoinreviews.org eude.es kegunaan nizoral cream despues de que tiempo hace efecto el misoprostol cytotec modo de uso combien coute le stromectole avmdtogo.org pazarlamacadisi.com zithromax online with mastercard flagyl sun sensitivity neutropenic fever levaquin augmentin foodloversheaven.com in celebrex commercial who is in the boat cyproheptadine appetite stimulant husband on zoloft ttc celebrex methodes de dosage creamost.com.py chatcufete.com microzide 12.5 mg skin rash duloxetine and libido adiconsult.pl piroxicam 10 mg side effects cattlespring.org how much amoxicillin for a seven pound cat africanamericanimages.us cialis online cheap no prescription levitra sales albuterol nebulizer steroid side effects eyes rizatriptan compared to sumatriptan cost misoprostol cytotec venta online paroxetine 25mg er verapamil hydrochloride sr 120 mg is a symptom of fluconazole pill dry mouth lisinopril 20mg how fast does it worj the cost of zovirax acyclovir spacecityparent.com cheap viagra india online bemylight.org foodloversheaven.com glucophage 250mg ciesielstwokukulak.com.pl nizoral treat hair lice kamagra suhagra generic viagra metoprolol 50 mg tablets erythromycin gel brand name philippines dutasteride is the best for bald how fast does celexa work efectos del lupron y tamoxifen hyzaar 100 25 mg pre?§o what is lisinopril hctz used for prozac sale uk NEOHAIRINDO.COM freelancer.info.pl harga obat nizoral pil does zofran kill fetus naproxen 800 azithromycin tablets price in pakistan phenergan dogs itchy skin shampo apa yg mengandung nizoral para que sirve el piroxicam gel 0.5 theitrecruiters.com can ciprofloxacin wash sperm out of the body celebrex urine smell sildenafil citrate ip levitra 5mg enough buspirone hunger buy orlistat ireland propranolol kopen viagra equivalent herbal tablets nexium mg 20 anafranil 25 mg drake obat apa does azithromycin kill sperm does nexium build up in your system cialis tablets cheapest fotografie-cursus.net is cialis d ang erous to t ake before surgery busy-autokary-wynajem.pl how long do amoxicillin side effects last hydroxyzine what dosage will kill you

previous  next  Title  Contents  Index        Previous    Next     Top   Detailed TOC 


10. Securing LAN/WAN Networks


Network security is vital. Many applications (IBM 3270 telnet emulation, Telnet, ftp...) send unencrypted passwords across the network. Although a network cannot be completely secured, the weakest links should be protected. It is not realistic to expect the Network to be ever 100% secure. The are two principal tendencies in network security today:

  1. New applications being developed are often designed so that they can transfer data securely across insecure networks. i.e. some type of authentication / encryption is built-in.
  2. IP level encryption (for TCP/IP networks) offers a secure channel between two machines, even over insecure networks. One example is SKIP (see the "Mechanisms" chapter).

Network security could easily be enhanced if Vendors replaced relics such as ftp, telnet and rlogin with more secure alternatives such as ssh (see the "Mechanisms" chapter), if NIS+ and/or Kerberos clients were bundled with all major OSs and a secure email system such as pgp were fully integrated into vendors email clients. But history shows that this is unlikely to happen.....

Centralised network management is important for maintaining network security. The Network (meaning both LAN and WAN) is analysed here in terms of:

11.1 Network Model (OSI)

The Open Systems Interconnect model is the standard for describing the transmission of data across networks. The seven layer model is particularly useful in comparing different architectures. The following diagram should help to understand the relationships between OSI, TCP/IP and communications layers used by Lan Manager.

osi_layers.gif (32196 bytes)

11.2 Network Protocols

11.2.1 Lan Manager / Microsoft Network / NT Domains

NetBEUI: Use only on local subnets.

WINS (Windows Internet Naming Service) allows Netbios name to IP address resolution via a highly automated dynamic database. It reduces the need for LMHOSTS files. See the "Windows NT" chapter.

RAS (Remote Access Service), see the "Windows NT" chapter. 

11.2.2 TCP/IP

11.2.2.1 Weaknesses

TCP/IP was not designed for high security:

However, TCP/IP is reliable, robust and the de-facto standard.

See the Mechanisms chapter for a discussion of new IP level encryption products designed to address many of the above problems. 

11.2.2.4 DNS (Domain Name Service)

11.2.2.5 NIS, NIS + (Network Information Service)

See the chapter "Securing UNIX". 

11.2.2.6 DHCP (Dynamic Host Configuration Protocol)

DHCP is very practical, especially for Laptops and in environments where reorganisations are constant. However, dynamic DHCP makes it difficult to uniquely identify machines, so for class  networks, avoid the use of dynamic IP addressing. Static DHCP may be useful for centralising the management of IP addresses.

11.2.2.7 NFS (Network File System)

See the "Securing UNIX" chapter for a discussion of NFS.

11.3 Physical network types

If confidentiality is a major concern, use fibre optics, they are very difficult to interrupt or sniff.

11.3.1 Ethernet

11.3.2 Leased lines

Copper leased lines should be hardware or software encrypted. 

11.3.3 FDDI

Because FDDI is a fibre optic ring, it is impossible to "listen" by detection of magnetic fields and if someone tries to connect to the ring, they need specialist equipment and the ring would be disturbed - it should not go unnoticed.

11.3.4 ATM

ATM (Asynchronous transfer mode) is a complex suite of protocols with many interesting features, such as bandwidth allocation, virtual networks, high speed... They are useful primarily by telecom providers. The complexity of ATM makes it difficult for hackers to crack, but also difficult to configure correctly.

11.4 Network Devices

Most attacks come from the inside, so:

On critical subnets, it's important correctly configure network devices: only enable needed services, restrict access to configuration services by port/interface/IP address, disable broadcasts, source routing, choose strong (non default) passwords, enable logging, choose carefully who has user/enable/admin access, etc.

11.4.1 Hubs

11.4.2 Bridges

11.4.3 Routers

Routers have become complex and can have almost as many configuration options as a UNIX host...

11.4.4 Modems

A sweep of all Internal telephone lines should be made once a month (during the night) to see how many modems are attached and at what numbers. This can then be checked against a list of registered modems. TBD: example of a product which can do this!

11.5 External connections to WANs

11.5.1 Permission for external connections

For external access (via modem for example) to internal systems or from internal systems to the outside (Internet for example), a user should have the written permission. The user should prove that such an external access is absolutely necessary.

These external connections can be classed as incoming and outgoing: 

11.5.2 Example Incoming connections

11.5.3 Example Outgoing Connections

11.5.4 Simple Internet or Bulletin board access

If Internet access is required for information browsing (e.g. ftp or Web) on a sensitive zone, one solution is to use a simple PC with modem but with absolutely no (internal) network connection.

It is important that these connections be registered with, and audited regularly by centralised security staff. 

11.5.5 Insecure subnets

Where many external connections are required in one building, one possibility is to group together the external connections on an "Insecure Subnet" which has direct outside access, but which is separated from the internal network via a Firewall. This minimises cost (only one firewall) and maximises flexibility, but great care must be taken in the daily usage on these machines on the "Insecure Subnet", as they must be considered as dangerous, penetrated hosts. 

11.6 Network Management / Monitoring

Networks are becoming more important, data speeds and volumes are increasing and networks are becoming more and more heterogeneous. Professional Network monitoring can help to analyse and predict problems (and increase availability). Such monitors can also be used to increase security by two methods:

a) "Strange" network behaviour could be an intrusion, so a monitor should be able to note "strange" (i.e. not "normal") network behaviour.
b) If security policy specifies that certain services are not to be used by certain hosts at specified times, network monitor software could be used to check this. e.g. if the security policy for a network specifies that ftp is not to be used between 00:00 and 06:00, then any ftp traffic on the network at this time should be monitored an reported as a security alert. This kind of monitoring is especially useful for local high security networks.


previous  next  Title  Contents  Index        Previous    Next     Top   Detailed TOC